Tnn AnERTcAN M rNERALocrsrJOI'RNAL OF THE MINERALOGICAI SOCIETY OF AMERICA

Vol. 10. NOVEMBER, 1925 No. 11

THE PARAGENESIS OF THE GRANITE PEGMATITESOF CENTRAL MAINE

Knr.txprn K. Laxons.* Haraard Uni.aersif'y

SUMMARY

A study of the paragenesis of certain pegmatites in centralMaine has caused the writer to advance the following ideas whichdiffe'r somewhat from those usually held on the subject. The

essential features of his thesis are:A. Minerali zation of the pegmatites was accomplished in succes-

sive stages. The minerals deposited during each stage composea distinct group or class.

I. During the first stage alone there was a mass crystallizationfrom the liquid phase. The typical minerals of this class are potash

feldspar (usually microcline), qnartz, muscovite, biotite, black

tourmaline, beryl, garnet, arsenopyrite, and manganapatite.II. This was followed at every deposit studied by a high temper-

ature hydrothermal phase. The volatile constituents of the magma,which played a rather minor part in the first stage, now become of

supreme importance. During the crystallization of successivelyIower portions of the magma the "mineralizers" are expelled and

work upward, depositing new minerals as they do so. While themagma at hand and at slight depth was crystallizing high tempera-ture conditions prevailed, and the first class of hydrothermalminerals resulted. Typical minerals of this period aret q'oartz(usually in crystals), cleavelandite, lepidolite, lithia tourmaline,columbite, cassiterite, spodumene, and etched or pocket beryl.

III. At Buckfield, and to a very minor degree at Mount Micaand Auburn, an intermediate phase followed during which rarelithium-manganese phosphates were deposited by the ascendingsolutions. Typical products of this phase are: amblygonite,lithiophilite or triphylite, rhodochrosite, eosphorite or childrenite,fairfieldite, and reddingite.

* Presented as part of the requirement for the degree of Doctor of Philosophyin the Division of Geology at Harvard University.

355

356 TEE AM EMCAN MINERALOGIST

IV. A final hydrothermal phase which was very well developedat Buckfield, Greenwood and parts of Auburn resulted in thedeposition of large amounts of cookeite and quartz. At Greenwoodand Auburn purple apatite crystals were also formed in abundance.Typical minerals are quartz, cookeite, and apatite.

V. Ground water alteration of material already present pro-duced the last class of minerals. The minerals of this type aremainly kaolin and montmorillonite. Locally manganese oxides,dahllite, and francolite were formed.

B. The pockets of the Maine pegrnatites are largely secondary,produced by dissolving activity of the same ascending solutionswhich deposited the rare minerals of the second and later clqsses.

INTRODUCTION

The granite pegmatites of central Maine have been describedin some detail by Bastin.l The present paper presents the resultsof a more detailed investigation of two recently opened depositsand some additional facts concerning some of the better knownlocalities.

Recent feldspar quarrying operations at Buckfield, in OxfordCounty, have uncovered a remarkable suite of minerals. Detailedstudy of some two hundred specimens from this locality now inthe Harvard mineralogical laboratories has resulted in the identi-fication of over thirty minerals, a half dozen of which appear inbut one or two other localities. This intensive study, coupledwith observations in the field, developed the thesis that theminerals were by no means products of one period of crystallizationbut group naturally into five classes. Although the result of apractically continuous process the classes difier from each otherin chemical, physical, and mineralogical character. Only oneclass, the first, solidified as a magma. The minerals of the mainpegmatite, mostly microcline and quartz, belong here. The nextthree classes represent successive waves of hydrothermal activityfrom the slowly cooling igneous mass beneath. The solutions werereplacive, dissolving the old and depositing the new. At timesthe former process exceeded the latter, and open spaces or pocketswere left, usually lined by drusy crystals. A gradual change in the

t Bastin, E, S. Geology of the pegmatites and associated rocks of Maine.U. S. Gecl. Sun, 8u1tr.445, 1911.

JOURNAL MINERALOGICAL SOCIETY OF AMERICA J J /

character of the solutions produced a sequence of minerals withina class. A more radical change resulted in the initiation of a newclass.

The first of these hydrothermal groups, Class II, is characterizedby cleavelandite, Iow temperature qtartz crystals, transparenttourmalines, and many other minerals. Here we find rnost of the"pocket" minerals prized by the collector.

Class III is a rare phase, present to any great extent only atBuckfield, Maine, and Branchville, Connecticut. The unusualphosphates lithiophilite, eosphorite, fairfieldite, and reddingitebelong here.

The Class IV minerals, chiefly cookeite, qtrartz, and apatite,are distinctly the result of a relatively late but active mineraliza-tion. This phase is developed to a considerable extent in severalof the central Maine pegmatites.

In Class V are placed the supergene alteration products ofthe minerals in the preceding classes.

Several mineral species appear in more than one class. But whenthis is true differences in either habit or physical, chemical, andoptical properties are found and the mineral may usually beplaced as definitely as though different species were involved.With beryl and apatite these difierences are indeed striking.

This, briefly, is the thesis advanced in the following pages. Thelocality used for illustration is Buckfield, for many reasons. Thecollections from here are most complete. The range of minerals islarge. The presence of one more class than usual, containing therare phosphates, makes the deposit of interest. F'urthermore,recent quarrying operations have made the interior of the pegmatiteaccessible for field study. The locality is a new one, practicallyundescribed in print.2

Briefer descriptions of parallel deposits follow. Greenwood,although completely Iacking the minerals of Class III, illustratesthe other classes well. The control of structure on the ascendingsolutions is better shown here than at Buckfield. Mount Mica andAuburn, two old and famous mineral producers, are likewisebriefly considered from the standpoint of paragenesis.

2 A very brief preliminary report on this deposit by Dr. Charles Palache waspublished in the March, 1924, Ameri.can Minerdogi,st.

358 TH E A M EMCA N M I N ERALOGI ST

Greenwoodo

rtL-and

*pegnatlte

g\lE-srAlmE ,ULE9--o t o 2 o 9 & F

Frc. 1. Southwestern Maine showing location of pegmatite bodies describedin this report.

LocerroN

A map showing the approximate location of the pegmatitesdiscussed is given on Plate I. The village of Buckfield is on theRangeley division of the Main Central Railroad. A dirt roadruns to the eastward to Paris HiIl and South Paris, the lattera town on the main line of the Grand Trunk. The Buckfieldpegmatite is on this road four miles from Buckfield village, and

t-l\I

' t

aqaxo

XEIITJECEC

,rlrco>

"%+

JOARNAL MINERAI.AGICAL SOCIETY OF AMEKICA 359

seven miles from South Paris. A private road at Bennett's farm

runs north from the main road three fifths of a mile to the deposit,

which caps a rounded, glaciated hill. The pegmatite body has

been opened up on the west flank of the hill by quarrying opera-

tions of the Maine Feldspar Company.The Greenwood deposit is located on the southwest side of

Noyes Mountain in the town of Greenwood, two miles south of the

village of that name, and eleven miles north of Norway. A trail

leaves the Norway-Greenwood road at the crossroads near the

foot of the mountain and climbs up 350 feet to the pegmatite.

An old producer of mineral specimens, this deposit was reopened

in the summer oI 1923 by the Harvard University Mineralogical

Department. The operations of that summer lowered the floor

of the quarry some fifteen feet and drove the breast back about

ten feet. The quarry is now idle.

FrBr,o aNo Laeonaronv Wonr

Active quarrying for feldspar has been going on at the Buckfieldquarry since the summer of 1923 and the writer made frequent

visits there during the summer and the following spring. In the

late summer ol 1923 Professors Palache and Larsen visited thequarry just after a large pocket had been revealed and they made

an extensive collection. Mr. W. D. Nevel of Andover, Maine, also

kept a close watch on the quarrying operations and most of his

collections were acquired by the Harvard Museum. All of this

material has been available for study.Operations at Noyes Mountain were begun many years ago by

Mr. George L. Noyes of Norway, Maine. The minerals he collectedwere largely preserved and passed into the possession of the

Harvard Museum, together with the lease of the property, in 1917.

fn the summer of 1923 active quarrying was undertaken by the

Harvard Mineralogical Department under the supervision of the

writer. Loren B. Merri l l of Paris, Maine, did most of the actualwork of excavation, and gave to it the invaluable experiencegained from a lifelong familiarity with similar deposits at Mt. Mica

and elsewhere in Oxford County.The bulk of the work was performed in the laboratory. Speci-

mens from both localities, especially Buckfield, have been studied

by the use of immersion liquids and the microscope, and by blow-pipe and chemical tests. The electromagnet and the Clerici heavy

360 TH E AMEMCAN MIN ERALOGIST

solution were employed to secure pure material for analysis. fnsome cases the quantities involved were so small that microchemi-cal methods were necessary. Particular attention has been paidto the order of formation and the associations of the minerals, forhere lies the clue to their genesis.

Eight of the more unusual minerals have been analyzed by MissHelen Vassar, the departmental chemist. These analyses bringout several points of interest and will be included with the mineraldescription.

Acrnowr,rncMENT s

The writer wishes to express his sincerest thanks for the helprendered throughout the work by Dr. E. S. Larsen, both in thedetermination of minerals and in the theoretical discussion. Manyof the ideas worked out and advanced here have long been hetd byDr. Larsen, especially those on the later albitization of pegmatites.

Dr. Charles Palache has afforded a constant inspiration through-out the course of this study. Through his aid the field work wasmade possible, and try his suggestion the study was made. Hehas not only devoted much of his own time to the study, but hasalso thrown the resources of the department behind it.

BUCKFIELD

Locer, Grorocv

Study of the local geology at Buckfield is made difficult by anextensive covering of glacial till. Gneiss bounds the pegmatitebody on the'east and south, granite on the west and north. Theformer is the country rock of the region while granite is morelocal in extent. In the hand specimen the biotite gneiss showsparallel bands of biotite with orthoclase and quartz between thebands. Minerals present to a minor extent are apatite and pyrite.The rock is a metamorphosed granite.

The granite is light colored and has a fine grained aplitic texture.It is rich in quartz and contains also essential oligoclase, micro-cline, and muscovite, a little biotite, mostly intergrown withmuscovite, and traces of garnet and hornblende. Occasionalsplotches of black tourmaline are present and it evidently under-went attack by portions of the still liquid magma as quartzencroaches on it extensively. The contact of the granite andgneiss was nowhere found but the unmetamorphesed character

JOURNAL MINERALOGICAL SOCIETV OF AMEKICA 361

bf the granite shows that it is much younger than the gneiss.

It is probably related magmatically to the pegmatite.

PBcuarrrr

DBscnrprroN

The pegmatite body caps a low hill and is flat or dips at a low

angle to the east. Its areal extent is large, the paced distance

from the footwall contact with granite on the west flank of the

hill to the gneiss'contact on the eastern slope measuring over five

hundred feet. At the top of the hill six hundred and fi.fty feet,

apparently all pegmatite, separates gneiss on the south from

granite on the north. This dimension may be considerably less

to the west, where exposures are lacking.Mining has proceeded on two levels. The upper terrace extends

from the surface back into the hill for about a hundred feet,

where, due to the natural slope of the hill it has a depth of about

thirty-five feet. The breast at this point is forty feet wide. A

second cut, f ifteen feet below, extends into",the'hil l for a lesser

distance.A small pit four hundred feet to the northwes! opens up pegma-

titic material exceptionally rich in beryl. The mineralogical

similarity between this deposit and the much larger one suggests

that they are related intrusions.The size of grain of the minerals in the main pegmatite varies

greatly. Adjacent to the contact with the country rock the

feldspar and quartz anhedrons are no larger than those in the

interior of the average granite. Outside the contact phase these

minerals appear in masses up to ten feet across. Some examples

of this latter size may be seen on the face of the quarry.

The minerals of the first class make up the main pegmatite and

are rather uniformly distributed, but those of later hydrothermal

deposition, belonging to Classes II, III, and IV, are confined to a

relatively small zone exposed in the lower workings of the quarry'

In opening up this level, the miners first passed through an area

of fallen or slumped pockets. Massive feldspar and quartz of the

walls were mixed with quartz crystals, some of large size, belonging

to a later generation. Surface waters had added a coating of clay to

the debris. As operations extended the cut farther into the hill,

and correspondingly farther from the surface, undisturbed pockets

were encountered.

362 THE AMERICAN MINERALOGIST

MBruon on Eupr-acpunNr

The pegmatite shows various features which indicate that itwas an igneous intrusion,

In the first place the size of grain is greatly diminished borderingthe contact rvith the country rock, implying a chilled phase aboutthe periphery of the magma. Furthermore, the minerals crystal-lized in a definite sequence, identical to that in a granite. Lastly,there are inclusions of gneiss in the pegmatite more or less resorbed.The evidence appears to be strongly in favor of deposition by aviscous rather than a highly liquid solution.

The presence of a higher percentage of volatile constituentsthan is customary in a granite resulted in a lower crystallizationtemperature, which permitted the formation of large crystals andthe complete conversion of orthoclase to microcline. But of fargreater importance was the post-magmatic activity of thesevolatile constituents in the formation of later minerals.

LnrBn Acrrvrry

It is the thesis of this paper that mineralization of the pegmatitedid not cease with the magmatic crystall ization just described,but continued for some time, through the agency of ascendingsolutions. These were expelled by minerals crystallizing fromsuccessively lower portions of the igneous mass. In their upwardand outward movement the hot solutions dissolved and replacedearlier minerals. Large pockets were formed, pre-existing mineralsaltered, and new minerals superimposed. The minerals of ClassesII, III, and IV were deposited by these solutions.

The bulk of the evidence in favor of a hydrothermal origin forthe minerals of these classes lies in their relationship with themagmatic minerals. Undoubted actual replacement of microclineby cleavelandite, an important product of the first hydrothermalstage, is described under the latter mineral. Other minerals ofClasses II, III, and IV definitely replace minerals of the mainpegmatite. In a similar way the later hydrothermal mineralsreplace the earlier. At Greenwood extensive silicification duringthe last stages of mineralization resulted in many quartz pseudo-morphs.

The ability to divide the minerals, due to their consistentassociations, into definite classes is regarded as evidence of aqueousdeposition. Direct igneous crystallization produces a sequence of

JOURNAL MINERALOGICAL SOCIETY OF AMERICA

mineralization, but the products are the result of one continuousphase. Deposition was probably fairly continuous in the centralMaine pegmatites, but changes in the character of the ascendingsolutions produced rather abrupt differences in the resultingminerals.

Further evidence of a hydrothermal origin is shown by thepresence of many minerals often found in veins. The high tempera-ture vein minerals, tourmaline, albite, topaz, and cassiterite, arefound in Class II. A low temperature vein mineral, rhodochrosite,is found in Class III. Likewise, in this and the next class, severalhydrous minerals appear, signifying low temperatures and abund-ant water.

Lastly, the fact that these minerals are limited in extent to arelatively restricted zone in the pegmatite (intersected by thelower quarry floor) suggests that they were deposited there bysolutions working along a local channelway.

The cavities, or pockets, are of great interest. Some ratherIarge ones have been uncovered in the central Maine pegmatites.

The largest pocket at Buckfield extended from the open cutback into the ledge, with varying course, for over twenty-five feet'

The pockets at Greenwood were smaller, although one measured

seven feet wide and ten feet long, with a depth of four feet. MountMica has been famous for its pockets, the largest of which was

20by 12 by 7 feet. The cavities vary from this extreme down to a

diameter of only a few inches. When found they are partially

filled with debris (pocket sand) which has scaled ofi from the walls

and roof.Writers in the past have ascribed the origin of such cavities in

pegmatites either to gas action or shrinkage during crystallization.In 1853 Delesse3 said:

It is then probable that the cavities are the result of the action of gases; their

forms and their character indicate, moreover, that the gases were set free at the

moment when the rock was sufficiently consolidated to preserve the cavities, but

when it was still so plastic that the minerals could develop very freely.

Brdggera states that drusy cavities result from contraction

3 Delesse, A., Sur la Pegmatite de l'Ireland, Bull. Soc. Geol. ile Fronce (2),10,

p. 570, 1853. Quoted by Kemp, The Pegmatites, Econ. Geol-, December L924.' Brcigger, W. C., Die Mineralien der Syenitpegmatitgiinge der Siidnorwegischen

Augit- und Nephelinsyenite, Zeit. Kryst. Min., 16, 1890. Sections on genesis

translated by Evans, Can. Rec. Sci., 6, pp. 33-46,61-71,1894.

364 THE AMERICAN MINERALOGIST

during crystallization. Miarolitic cavities are filled by both latemagmatic crystallization and by minerals formed by special"agents mineralizateurs. "

A few years later Crosby and Fullers expressed similar views:

. . . . while a higher degree of local hydration gives rise to the concentric crystalline

shells and shrinkage cracks (pockets) with the highly perfect crystallizations of

feldspar, quartz, fayalite, etc., characteristic of the typical lithophysae.

On the subject of miarolitic cavities Bastino says:

Such cavities have been attributed by various writers to shrinkage of the

pegmatite mass in crystallization. This may, in fact, play some part in their forma-

tion, but that they are not entirely the result of shrinkage, but, on the contrary,

were filled or partly filled with some material which has since disappeared, is shown

by the presence of periectly developed crystals of quartz, tourmaline, and other

rninerals projecting inward from the walls of the cavities. Some filling must have

been present from which such crystals derived the materials for their growth. It

is probable, therefore, that immediately after the crystallization of the main body

of pegmatite the miarolitic cavities were completely filled with a gaseous solution

which may later have liquifed and has since disappeared. Water carrying numerous

other substances in solution probably formed the bulk of this cavity filling. The

abundance of quartz crystals on the walls of these cavities indicates that silica

was one of the most abundant of the dissolved substances.

It is the writer's opinion that most of the pockets in the pegma-

tites of central Maine are secondary in nature, due to dissolvingactivity on the part of the ascending solutions, rather than primarygas or contraction cavities in the ign'eous magma. This conclusionis based upon the following lines of evidence:

1. Shape of pocket. The larger cavities are extremely irregularin shape. The dimensions of the largest one at Buckfield wereSl Ay S\ by 25 feet. This tunnel-Iike opening follows a tortuouscourse and constantly varies in diameter. In describing a similar

cavity at Greenwood BastinT says: " . numerous small lobesadd irregularity to its form." The largest pocket at Mount Mica

contained three connecting chambers.s Surely there is nothingbubble-like or otherwise suggestive of gas cavities about suchopenings as these. In their irregularity they more nearly resemblelimestone caves, which result from the dissolving activity ofground water.

5 Crosby, W. O. and Fuller, M. L., Origin of Pegmatite, Am. Geol., 19, p. 172,1897.

s Bastin, E. S., Geology of the pegmatites and associated rocks of Maine, U. S.Geol. Surr., Bull., 445, p, 32, l9ll.

7 Loc. ci . l . , p.71. 8 Loc. ci t . , p. 86.

JOARNAL MINERALOGICAL SOCIETY OF AMEKICA 365

2. The cross-cutting relationship of the pockets to the mineralsof the main pegmatite. The cavities cut through the pegmatiteas do dikes across sedimentary strata, with equal disregard forpre-existing structure.

3. Actual solution of microcline. Specimens of massive feldsparfrom Buckfield show unmistakable evidence of severe corrosion.Plate I, A pictures one such specimen. The microcline has beenirregularly dissolved away, and the cavity walls are lined withhydrothermal minerals.

Corrosion of a similar nature has been noted by Lacroix:eUp to this period of fcrmation of the rock it seems ttrat the phenomena of

crystallization were products of a continuous phase, with onll' the changes ofchemical composition in the fluids circulating in the vein;these phenomena have

been essentially constructive. But, there arrives a moment where a discontinuity

intervenesl the minerals thus formed are no more found to be in equilibrium with

the medium. They are subject then to corrosion and transformation.The great crystals of microcline have been profoundly corroded, attacked, in

particular following their planes ol cleavage, Cavities contain Iater albite, tourma-

line, and lepidolite.

4. Anhedral forms of the magmatic quartz and microclineadjacent to the pockets. These minerals were prevented fromassuming crystal boundaries in the main pegmatite by the latenessof their crystallization. But where they formed adjacent to a gas

or shrinkage cavity one would expect crystal faces to be developed.

Quartz crystals do line the pocket walls, but they are of a latergeneration. In the pockets under discussion microcline never has

crystal boundaries.5. Pseudomorphs. At Greenwood many qttartz pseudomorphs

have been found. The quartz was deposited about earlier minerals

during the last hydrothermal stage. In most cases the mineralsserving as host have been completely removed. This shows power-

ful dissolving activity toward the close of the hydrothermal period

at least.6. Invariable association of hydrothermal minerals with the

large pockets. The secondary pocket zone is absolutely identicalwith the zone ol hydrothermal minerals. This is to be expectedif the same solutions were responsible for both.

The German writers, Laubmann and Steinmetz,lo describe

pegmatite cavities which they believe to be secondary:

g Lacroix, A. Mineralogie de Madagascar, Vo]. 2, p.310, 1922.r0 Laubmann, H. und Steinmetz, H., Phosphatftihrende Pegmatite des Ober-

pfiilzer und Bayerischen Waldes, Zeit. Kryst. Min.,55,584, 1915-1920

366 TH E AMEKICAN MI N ERALOGI ST

The distinct drusy development of these pegmatites as well as the magnificent

crystal development in the druses, is secondary and brought about through the

destruction of the rock.

The possibility of cavities due to shrinkage or gas bubbles is

not denied. It may be true that some or all of the secondary

pockets in the central Maine pegmatites are merely much enlargedprimary cavities.

The pockets grew in size with each wave of hydrothermal

activity and at the same time minerals were deposited, a difiereotgroup for each period. Three such groups appear at Buckfield.

The last activity was that of the surface waters forming the

supergene minerals of Class V.

CnBurcar. CnenacrPn

The chemical character of the pegmatite varies with its difierent

phases. In the earliest phase the mass composition of the pegma-

tite magma was the controlling factor. This magma was very similar

chemically to a granite magma, so the composition of the resultingpegmatite is close to that of a granite. Unusual amounts of l i thium,

manganese, and glucinum resulted in the formation of lepidolite,

manganese apatite, and beryl among the magmatic minerals.

With the completion of the magmatic crystallization and the

subsequent hydrothermal activity the rarer elements of the

magma are relatively more abundanl while potash and alumina

correspondingly decrease. Silica remains quantitatively importantin Class II, almost disappears in Class III, and returns in large

amounts in Class IV.In Class II we find the greatest variety of elements and minerals'

The hydrothermal solutions carrying the residual liquor of the

magma were loaded with all the elements of the original magma,

except potassium and arsenic. Many elements appear in Class II

which were lacking in Class I, and some of these, such as caesium,

columbium, tantalum, and tin, do not appear in any later class.

No new elements were introduced after the close of this earliest

hydrothermal stage. From a chemical standpoint this class may be

called the silica-sodium-rare element phase.The Class III minerals represent a lithium-manganese-phos-

phorus phase. These three elements were in the magma in unusualquantities and became increasingly important as the mineraliza-

tion progressed from Class I to Class III. Manganese and phos-

phorus reached their climax here, but l i thium did not.

TOURNAL MINERALOGICAL SOCIETY OF AMERICA 367

Hydrothermal activity closed with a lithium-silica phase, which

produced the minerals of Class IV.Chemically combined water first appeared in Class II and in-

creased in importance through Cla'sses III and IV. Supergene

water combined with hypogene elements to make many of the

minerals of Class V.

MINERALS OF CLASS I

The minerals of this class make up the main body of the pegma-

tite and at most localities they stand alone, there being no evidence

of later activity. At Buckfield many later minerals are found, but

they represent a very small proportion of the total mass.

The minerals of Class I crystallized from a magma. The analogy

to a granite is apparently also followed in the order of formation.

The first to complete their crystallization were the accessories

garnet, beryl, tourmaline, and apatite. Then came feldspar and

lastly, qtartz.Physically the minerals were (and still are where removed from

the zone of later activity) tightly intergrown and no interstitial

open spaces were found which were left by this primary crystalliza-

tion. In the relative size of grain the pegmatite does not difier

widely from a granite. White the apatite, tourmaline, mica, and

garnet crystals are several hundred times their customary size in a

granite, so are the feldspar and quartz masses. A possible exception-

is beryl, which does not appear in granite.

MrcnoclrNB

Microcline is the most abundant mineral at Buckfield. The only

other feldspar detected- in Class I was albite, in perthitic inter-

growth with microcline. Potash feldspar, although of extreme

importance here, does not appear in any of the later classes.

On the freshly cut quarry face microcline stands out prominently

due to its white color and large cleavage faces' Some of the latter

are two meters or more across and the grain varies from this,dimension to about half a millimeter in the contact phase. Later

dendrites of a black manganese oxide appear on many of the cleav-

age faces.Kaolinization of the microcline has been very slight, as seen

under the microscope. The characteristic albite and pericline

twinning is commonly absent, but the 15o extinction angle on the

base distinguishes it from orthoclase.

368 TEE AMERICAN MINERALOGIST

The feldspar appears to have completed its crystallization afterall the other minerals save quartz. It encloses euhedral crystalsof beryl, tourmaline, and garnet and is itself surrounded bymassive qtJartz.

Potash feldspar, usually microcline, is a leading mineral in thegranite pegmatites of central Maine, and elsewhere.

Quanrz

Quartz is next in abundance to microcline. It appears in largegray masses equal in dimension to those of feldspar. Nowhereare crystal boundaries developed.

As in a granite the final crystallization of the quartz completedthe solidification of the magma. Therefore, none but anhedralforms were possible, and those surround and enclose all of theother constituents. At the top of the hil l a series of six-inchquartz veins with parallel strikes cuts the main pegmatite.

Aparrrn

Apatite appears scattered through the microcline in dark green,opaque, somewhat spherical anhedrons from a fraction of a milli-meter up to fifteen millimeters in diameter and is clearly of latecrystallization. Under the microscope it is almost colorless. Itsindices of ref ract ion are: o:1.642+.003, e :1.639+.003.

Chemical analysis shows the mineral to be manganapatite,as it contains 8.69 per cent MnO. The complete analysis byMiss Vassar follows:

i;3' t;::'""""'FerOs 0.55MnO 8 .67F 3 . 8 0clAl2osHrO 0 .06

101 .84F : O 1 . 6 0

100.24 per centAnalyses are given in Dana's System of Mineralogy for eight

manganapatites, only one of which definitely contained moreMnO than this. A dark green apatite from Branchville, Connecti-cut , had 10.59 per cent MnO.

JOURNAL MINERALOGICAL SOCIETY OF AMERICA 369

I'his particular apatite is less common in the other central Mainepegmatites. In his description of Mount Mica Bastinll says,

"Apatite occurs in the solid pegmatite in irregular opaque green

masses, some few of which weigh a couple of pounds." Apatite ofthis character was observed at Greenwood, where the mineral is

also exceptionally abundant as the product of a later mineraliza-tion.

BBnvr

Beryl is common in quartz and feldspar at the northwest cornerof the large quarry, and appears in even greater abundance in thesmall open cut four hundred feet beyond. Here hardly a squareyard of the pegmatite face may be found which does not containa section of a beryl ciystal. The crystals are strongly prismatic,up to eight centimeters in diameter and twenty centimeters long.Some odd shapes appear. One crystal abruptly doubles its di-ameter, without displacing the vertical axis. Several crystalsexhibit a decided tapering along the prism zone. The color rangesfrom bluish green to green, usually somewhat mottled. All in thisclass are opaque or translucent.

TouRuar.rNp

Tourmaline of the first class is here as in most pegmatites blackand opaque and appears in well-defined prismatic crystals scatteredrather widely through the main mass of the pegmatite. Some ofthese reach ten or twelve centimeters in diameter and twentycentimeters or more in leneth.

lunroorrttIn the main pegmatite lepidolite has all the appearance of

muscovite. It occurs in silvery white books, usually five to eightcentimeters in diameter and under one centimeter in thickness.Optically lepidolite is almost identical with muscovite, so theflame test was used in distinguishing these two micas. The whitemica of the first class gave as sharp and as definite a lithium flameas did the pink lepidolites of the later classes. The flame wassecured all about the periphery, in the center, and in every quad-rant of the book. Also the plates were microscopically homo-geneous. Nowhere was there any evidence of lepidolite-muscovite

tr Loc. cil., p. 88.

370 THE AMEKICAN MINERALOGIST

zoning or intergrowths as described in specimens from HaddamNeck.l2 No muscovite could be found among the specimensfrom Buckfield.

Lepidolite also was produced to a minor extent about the biotitegneiss xenoliths found near the contact. Reaction between thebiotite of the xenolith and the enclosing lithia-rich magma resultedin a zone of lepidolite 6 millimeters wide between the two.

The mica of Class I is usually muscovite as is the case at Green-wood and Mount Mica. Evidently an unusual concentration oflithium in the pegmatite magma existed at Buckfield. Lepidoliteoccurs in the normal pegmatites in Madagascar.r3

Brorrrp

Biotite is an accidental constituent of the pegmatite, beingintroduced by the inclusion of fragments of bi.otite gneiss countryrock. Working over by the magma produced a chemical andphysical change in the biotite. The flakes are larger than they werein the gneiss, and lithium has been incorporated, due to its greatabundance in the magma.

The biotite is black with a most peculiar intergrowth of plates.These are all arranged parallel to one of two directions in thexenoliths. As the changes in direction are minutely spaced theresult is two perfect cleavages, at right angles in one xenolith, andat approximately l2}o in another.

Genwor

A brownish red garnet is a very minor accessory in the mainpegmatite. Judging from its index of refraction, color, and asso-ciations it is very likely spessartite which is very common in thepegmatites of Maine.

AnsBNopvnrre

Only two specimens containing arsenopyrite were found. Inone it occurred in parallel bands 1 to 5 millimeters thick. Betweenthe bands were even narrower zones of brown lepidolite. The latterwas in plates about 5 millimeters across which were arrangedparallel to the banding. The whole is tightly enclosed in massivemicrocline and quartz.

12 Bowman, H. L., Occurrence of Minerals at HaddamMi,neral.og. Mag., May 1902.

ra Lacroix, A., Mineralogie de Madagascar, Vol. II, p. 304,

Neck, Connecticut,

1922.

JOURNAL MINERALOGICAL SOCIETY OF AMEEICA 37t

In the second specimen arsenopyrite appears in crystals andsmall masses in the finer grained pegmatite adjacent to the contact.Associated minerals are microcline and lithium biotite.

Either arsenopyrite or ldllingite, the sulphur free iron arsenide,occur in most of the central Maine pegmatites. The former waspresent sparingly at Greenwood. Both were found at Mount Mica.

AMnLvcoNrrr

Amblygonite is very rare in the main pegmatite, appearing in butone hand specimen studied. Here it is a small cream coloredfragment intimately associated with manganese apatite, tourma-line, and white lepidolite.

Amblygonite has been reported from Mount Apatite and MountMica, from the latter locality in some abundance.

MINERALS OF CLASS II

Soon after the close of the magmatic period hydrothermalactivity set in and the minerals of Class II were formed. The more

unusual elements of the magma now come to the fore. Beside

silica the solutions of the first stage carried unusual amounts of

sodium, lithium, and th.e rarest elements. Many of these last

were soon exhausted so do not appear among the constituents of

the minerals in the later classes.The temperature at which the minerals of Class II were de-

posited was considerably below that in efiect during the magmaticperiod. The presence of low temperature qtartz places it below

575'C. But the temperatures were sti l l high in terms of hydro-

thermal mineralization. This is shown by the presence of such

typical hig.h temperature vein minerals as tourmaline, albite,

topaz, and cassiterite.The upward moving solutions dissolved away the minerals

of the main pegmatite, producing pockets. In the pockets many

minerals were deposited, some as drusy linings, others enteringinto and replacing the walls, while still others may have been

formed without attachment, in the free liquid fiIling the pocket. w/

The minerals of Class II may be divided upon a basis of quanti- .-

tative importance into three major and ten minor minerals' The

three major ones are quartz,lepidolite, and cleavelandite. Quartzwas the first to form, cleavelandite the last. These are the char-

acteristic pocket minerals of granite pegmatites.

I

372 THE AMERICAN MINERALOGIST

The minor minerals were all formed before cleavelandite, andsome even before quartz. In most cases their exact position isunknown because of the scantiness of their occurrence.

Quanrz

Quartz crystals of hydrothermal origin appear in a multitudeof sizes and shapes and vary from colorless to milky or smoky.Euhedral crystals of the low temperature type are the rule.These may be perfect crystals, with equally developed prismand rhombohedron faces, or they may be flattened and distorted,usually parallel to a prism face. Many of the crystals are under2 centimeters in length while a few attain lengths of over 2 meters.The majority fall between these two extremes. Crystal groupswere common at Buckfield. One of these, measuring about 40centimeters across, consisted of three quartz crystals whose prismscompletely merged, giving a massive base to the specimen. Onlythe smaller crystals are colorless. The large ones from this localityare almost always milky. Smoky crystals are exceptional.

The Class II quartz crystals line the pocket walls in greatabundance. They were seen on the walls of the big pocket andgroups of large crystals were common in the region of slumpedcavities intersected by the lower quarry floor. Quartz is the mostspectacular of the pocket minerals at Buckfield, due to the abund-ance and size of its crystals, the variety of its forms, and its drusyoccurrence. On the basis of form alone may the hydrothermalquartz be distinguished from the magmatic variety. The latter isnever euhedral, while Class II quartz is rarely otherwise. Asso-ciated minerals are cleavelandite and lepidolite. Quartz formedbefore these minerals, for the latter are often found clinging to thesides or partially rooted into the quarLz crystals.

Lnpiror.rrB

The lepidolite of Class II has the characteristic lilac color. Itappears in books usually under a centimeter in diameter and upto three centimeters thick.

Hardly a spccimen containing minerals of Class II fails to showlepidolite. Furthermore, it was one of the most stable of thepocket minerals as in many specimens the only remnants of thefirst hydrothermal stage are a few flakes or small books of lepido-Iite, the later solutions havins dissolved or replaced the associatedminerals.

JOURNAL MINERALOGICAL SOCIETY OF AMERICA 373

Pocket lepidolite may readily be distinguished from the earlier

variety. It is generally lilac rather than white in color. The books

are small and in most instances were formed in open spaces. The

much larger books of Class I lepidolite are tightly enclosed and

often subhedral.All the pocket-bearing pegmatites in central Maine contain

Class II tepidolite. It was probably more abundant at Mount

Mica than at any of the other localities. The constant association

of lepidolite with pocket tourmaline is well known to the gem

hunter.CrnavBr-auotrn

The platy variety of albite, cleavelandite, is one of the com-

monest pocket minerals. It is not found outside of Class II and is

therefore an unfailing index of the first hydrothermal period. The

Buckfield cleavelandite is found in single crystals, sheaves -ofplates, and fan-like aggregates. It is white and usually translucent

although one group contained several parallel transparent crystals.

The plates vary in thickness from very minute up to 8 millimeters

but most are considerably under 3 rnillimeters.The crystals of cleavelandite are invariably twinned on the

albite law. One group showed crystals oI sufficient perfection to be

measurable and the following forms, some of them-quite rare,

were ident i f ied: D(010), c(001) , m( l l } ) , M( l I9) , z(130) , r (403) ,

y(20r), p(rrr), g(22r), u(22t) , o(++s\, and. yQ4l. The habit ofthese crystals is unusual for albite owing to the prominent develop-

ment of the dome r(403) and the pyramid o(443) which truncates

its edge with the pinacoid.Cleavelandite usually replaces earlier minerals, although it may

also fill open spaces. One of the easily replaced minerals was

microcline. Several specimens were found with veins of cleave-

landite through the microcline. The depositing solutions had

worked into cleavage cracks in the magmatic feldspar and the

cleavelandite replaced outward from this plane of weakness. One

of these specimens is shown in Plate I B. Cleavelandite replaces

quartz also. Many of the pocket crystals of quartz have been

entered by blades of this mineral. In fact aggregates of cleave-

landite largely filling open spaces usually anchored themselves

in this manner.All of the pocket minerals are closely associated with cleave-

landite. Quartz and Iepidolite are the commonest of these. The

374 THE AMERICAN MINERALOGIST

rarer minerals, tourmaline, columbite, spodumene, apatite, etc.,are found either embedded in or adjacent to cleavelandite. Thelatter appears to have been the last of the Class II minerals toform.

Platy albite was equally important among the pocket mineralselsewhere. It was found in fair amounts at Greenwood, MountMica, and A.uburn. In every case cleavelandite was a product ofearly hydrothermal activity. This mineral is a most importantcriterion of the proximity of pockets.

Bnnyr

The beryl of Class II rarely exhibits crystal boundaries. Itssolubility in the Iater solutions has usually resulted in a severeetching, which has destroyed the outlines of the original crystal.These etched forms are known as "pocket" beryls, because oftheir characteristic occurrence in the vugs of pegmatites.

One white transparent crystal was evidently partly buried inthe wall and partly emergent into the pocket, for one-half thecrystal is highly etched, while the other half is unharmed, withcrystal boundaries intact.

Another larger crystal shown in Plate II A survived the attackof the later solutions even better. This crystal is about 10 centi-meters long and 15 centimeters in diameter. The first order prismand basal pinacoid are dominant, the second order pyramidsubordinate. The faces of the last form are etched. The crystalis pale aquamarine in color and unusually transparent.

The pocket beryls vary in color from pale green or colorless towhite and pink, and are always far more transparent than thegreen or blue beryl of Class f. Besides these differences the berylsof Class II vary from the magmatic crystals in specific gravity andin indices of refraction, as shown below:

Class I Class IIspecific gravitv

,.sr1'l1oo, i rtr"-rir-;e 1.575+ .003 1.590+ 003

The higher specific gravity and indices of refraction are probablydue to an unusual amount of alkalis, especially caesium. Thepresence of caesium in the ascending solutions is shown by theoccurrence in this class of pollucite, a caesium silicate. Pocketberyl is known throughout central Maine as caesium beryl, dueto the presence of caesium in beryl of this t ype from Hebron.

TOARNAL MINERALOGICAL SOCIETY OF AMEEICA 37s

Class II etched beryls are common at Greenwood and some goodcrystals have been found in the pockets in the pegmatite onMount Mica.

TouRu,q.rrNr

One of the first pockets opened at Buckfield contained two finegem crystals of tourmaline, five centimeters long. Many smallclear green unattached tourmaline crystals were found later. A fewvery small crystals also appear among the lepidolite, cleavelandite,and quartz specimens. In one of these a needle-like tourmalineis included within a quartz crystal, making the tourmaline defin-itely earlier in age.

Study of the pocket tourmaline crystals from Buckfield andelsewhere shows that some worked into the walls, replacing earlierminerals, but many more grew out from the walls, one end at-tached, the other free. Subsequent movements, perhaps some-times those due to the blasting of the quarrymen, often shookthese crystals free, and they fell to the bottom of the pocket.Here they are found loose, mixed with the other debris of thepocket. Sometimes very thin needle-like and doubly terminatedtourmalines are found in this pocket sand. Such an occurrencewas observed by Dr. Palachela at Haddam Neck, Connecticut.These crystals were probably never attached, but were formedin the solutions which filled the pocket during the first hydrother-mal period, and were left free in the bottom of the pocket with thepassing on of the solutions.' The tourmaline of this class difiers strikingly from that belong-ing to the magmatic period. It is green and transparent, whereasthe tourmaline of Class I was black and opaque. The gem tourma-line is a result of early hydrothermal activity rather than theproduct of magmatic-crystallization and contains more lithia andless iron than the black tourmaline of Class f. An increase inalkalis and a corresponding decrease in iron apparently causeincreased transparency.

Class II tourmaline crystals were common at Greenwood andin some of the Auburn quarries, but it was at Mount Mica thatthe mineral was most abundant. The large clear green and pinktourmalines from this locality have made it famous.

r{ Verbal communication.

376 THE AM EKICAN M I NERALOGIST

SpopuuBNn

Most of the spodumene at Buckfield has been rather completelykaolinized. Some of these pseudomorphs are about eight centi-meters long and half as wide. They are white and fibrous, exhibit-ing the exact structure (cleavage and parting) of the originalmineral. A little Iithium is present, undoubtedly due to residualspodumene.

Spodumene pseudomorphs occur closely associated with cleave-landite and Class II lepidolite. The original spodumene formedafter the lepidolite, sometimes completely enclosing it.

Veins of lepidolite, belonging to a later period of mineralization,cut through several of the kaolinized spodumene specimens.Others have been irregularly stained along the planes of separationby a black manganese oxide.

Much larger and fresher crystals of spodumene were found atGreenwood. Bastinls says that spodumene is "common in manyof the coarser pegmatites, especially those that carry gem tourma-lines, lepidolite, and other l i thia minerals."

Aparrrn

Apatite is comparatively rare among the minerals of Class II.ft appears in small green translucent crystals, prismatic in habit.Assuciate+ minerals are eleavelandite, lepidolite, and columbite'The apatite crystals are well developed and were formed pre-viously to the enclosing cleavelandite. This apatite is ratherdifferent from the earlier magmatic apatite. Although both aregreen, the later apatite exhibits defi.nite crystal boundaries and is

translucent whereas the apatite of Class I is always anhedral,cloudy, and usually occurs in much larger masses.

Pocket apatite of this generation is not uncommon in thegranite pegmatites of central Maine, but the drusy apatite appear-ing in great abundance at Mount Apatite and Greenwood belongsto a later period of hydrothermal activity.

HBnpnnnB

Several pale green crystals of herderite were found embeddedin cleavelandite. Others either clung to the sides of lepidolitebooks, or partially enclosed them; hence the mineral must have

15 Bastin, E. S., Geology of the pegmrtites and associated rocks of N{aine,

U. S. GeoI. Surt . ,8u11.,415, p. 18, 1911.

IOTIRNA'L MINERALOGICAL SOCIETY OF AMERICA J l I

been deposited after the lepidolite but before the cleavelandite.The largest crystal is 4 centimeters long, 1.2 centimeters wide,and a centimeter thick, but most are about a centimeter long.Many of these smaller ones are twinned.

Herderite was relatively insoluble during the later hydrothermalactivity, for one specimen consists of a small vug containingherderite and lepidolite crystals completely surrounded by quartzand cookeite of Class IV. This is the remnant of a pocket and itsminerals established during the first hydrothermal period.

Herderite is a rather rare mineral. In this country it is found atStoneham, Hebron, Greenwood, and Auburn, Maine. ' l i r: ' . : .,

Coruutrrp

Black, platy and prismatic columbite crystals up to 5 centimetersin length were occasionally found, usually embedded in cleave-landite. The latter is distinctly later, as it pierces the columbite insalients and veins. A bright purple oxidation product coats manyof the crystals.

Compared with its associates columbite was very insoluble inthe later solutions. Therefore it is often found in residual remnantsenclosed in minerals of a much later generation.

Small amounts of columbite were noted at Greenwood, MountMica, and Auburn. It is widely distributed in New Englandpegmatites.

MaNcaNoraNTALrrE

A few small masses of manganotantalite appear, encroachedupon and surrounded by quartz, cookeite, and apatite of Class IV.They are all under one centimeter in diameter, and in most in-stances have lost their crystal boundaries, due to the extensiveattack of the solutions depositing lhe later minerals. With theexception of a few flakes of lepidolite the associated Class IIminerals succumbed to this attack, and the manganotantalite andlepidolite are the only remnants of the earlier mineralization.

The Buckfield manganotantalite is dark brown and slightlytranslucent. Its gravity is 7 .29. Under the microscope the mineralappears yellow in color with no pleochroism discernable. It isbiaxial positive, with n approximately 2.2. Columbite has higherindices of refraction, lower specific gravity, and is more opaque.The common ferrotantalite is pleochroic and darker colored.

378 TH E AMERICAN MI N ERALOGIST

Manganotantalite from Mount Apatite has been described bySchaller.r6

CasstrnRrrn

Cassiterite, a fairly common accessory mineral in granite pegma-tites, is represented in the Buckfield collection by an isolated blackpyramidal crystal about two centimeters long. No other mineralswere attached to it to give a clue to its place in the genetic classifi-cation. It was however placed here in Class II because of itsassociations elsewhere.

At Mt. Mica cassiterite was not uncommon in cleavelandite andin the pocket sand. ft was also so found at Greenwood and inmost New England pegmatites.

Por,rucnB

A few small fragments of this rare mineral, a hydrous caesiumaluminum silicate, were found at Buckfield. It is white and glassyand lacks any very striking physical characteristics that aredistinctive. The only associated mineral is lepidolite, in veinform and obviously much later.

While pollucite has been found in small amounts in several qf

the Maine pegmatites the only abundant occurrence of it is inDudley's ledge, also in the town of Buckfield and about two anda half miles south of Bennett's ouarrv.

' Topl.z

The single crystal of. topaz found at Buckfield is a prismaticindividual about 5 centimeters long and four in diameter. It showsfaces of basal pinacoid and brachydomes which are coated withfine scales of purple lepidolite belonging to Class IV. The commonoccurrence of topaz with cassiterite and with cleavelandite as atStoneham is the reason why it is here placed in Class fI.

Two UNxwowN PHosPHATES

Two unidentified minerals were found mixed with quartz andlepidolite in one specimen. Diftculties encountered in theirseparation prevent a complete desgription at this time. The twoare intimately associated and megascopically the aggregate lookshomogeneous. It is white to colorless, quite vitreous and has ahardness of about 5.

16 Schaller, W. T., Mineralogical Notes, U. S. Geol. Su.nt., Bull., 490, p.95, 1912.

JOURNAL MINERALOGICAL SOCIETY OF AMERICA 379

Under the microscope the more abundant of the two minerals isfound to have a good cleavage parallel to the base. Many of theparticles contain minute rectangular inclusions with much higherindices. This mineral has the following optical properties: Uni-ax ia l f , c , r : 1 .591 , e :1 .606 .

An incomplete chemical analysis was made by Miss Vassar ona sample of this mineral which contained a small amount oflepidolite. The results are given below:

PzOs 31.99 per centsio2 3. t0HzO 16.39CaO 1.83MnO .10

i:3' "'1391.32 per cent

The alkalies may account for the missing nine per cent and if thisis true the mineral is a hydrous phosphate of aluminum and thealkalies.

The second mineral is biaxial negative, but with 2V small.The i nd i ces a re : c :1 .640 , A : I . 656 ,7 : t . gg1 .

Definite microchemical tests proved the mineral to be a phos-phate.

The optical data on neither of these minerals agree with thosegiven for any phosphates listed in Larsen's tables. Final determin-ation must await further work in separation and analysis.

MINERALS OF CLASS III

A second wave of hydrothermal activity produced the mineralsof Class III. This mineralization represents a lithium-manganese-phosphorus phase in the ascending magmatic waters. At Buckfieldseven minerals were formed, the majority of which are very rare.The phase itself is unusual in pegmatite formation and it is foundelsewhere in this country developed to any degree only at Branch-ville, Connectiout.rT Pegmatites containing phosphate mineralsin which iron predominates over manganese are found in France,t8and in Rabenstein, Bavaria.le

17 Brush, G. J., and Dana, E. 5., Am.,/. Sr., 16, pp. 33-46 and, ll4-123, 1878.lE A. Lacroix, Mineralogie de Madagascar, Y ol. 2, pp. 292 and 293, 7922.re Laubmann, H., and Steinmetz, H., Loc. Cit., p, 570,

lrd

(-)t l

Solution Break 1 I

Q

lll'BH

O

oa

;a; o.a : a

> c l Ev o

o

d

o

@

o

d

a

F

JOURNAL MINERALOGICAL SOCIETY OF AMEMCA 381

The minerals of Class III were deposited in a definite sequence,with but little chemical change from one mineral to the next.A slight difference in the character of the ascending solutions wouldcause an earlier mineral to become unstable and a new one to bedeposited. The later mineral probably grew at the expense ofearlier minerals, incorporating in itself some of the materialdissolved from them. A tabular view of the chemical and mineral-ogical changes occurring during this period is given below. Theminerals are listed in the order of their formation and the lowerhalf of the table includes similar minerals of Class IV and thesupergene minerals of Class V in order to show the time relationsof the whole phosphate group.

Lithium disappears as a mineral constituent after the formationof lithiophilite and triphylite and does not reappear until Class IV.Manganese is of utmost importance in all but the first mineral.fron is very subordinate, as the chemical analyses will show. Onecarbonate, rhodochrosite, interrupts the sequence of phosphates.

Most, ii not all, of the Class III minerals were deposited underlow temperature conditions. Rhodochrosite is typical of shallowveins as are the hydrous minerals.

The method of mineral formation varied during the period asin the first half replacement was the general rule while lateropen space filling became dominant, although the minerals wereoften replacive in character also.

Other evidence than temperature difierences place the Class IIIminerals later in age than those belonging in Class II. In one speci-men actual superimposition of minerals was observed. Herelithiophilite, a leading mineral of Class III, is definitely replacingspodumene, one of the minerals typical of Class II.

AMBrycoNtrB

A grayish white rim surrounds the pocket minerals of Class III.The border is about 4 centimeters wide, and usually consists ofmaterial microscopic in dimension. The rim is always bounded onthe outside by massive microcline of the main pegmatite. It isevidently caused by a replacement of the microcline.

Optical study and chemical tests proved the replacing mineralto be amblygonite. Residual fragments of microcline surroundedon three sides by amblygonite may be seen along the outer marginof this zone in the thin section. Clea-vage cracks in the feldsparare filled with amblygonite.

382 TH E AM EKICAN MI NERALOGIST

The main Class III mineralization was preceded by an ambly-gonite stage, during which this mineral advanced outward into themain pegmatite, replacing microcline as it did so. In a few speci-mens replacement has been complete, and the amblygonite iscoarse enough to show cleavage and yield good blowpipe reactions.

Optical difierences serve to distinguish amblygonite of Class IIIfrom that of Class I, as shown below:20

Class INegative

2V:approx .80oc : 1 . 5 9 6 + . 0 0 3F : 1 . 6 0 7 + . 0 0 3ry :1 .617 + .003

Class IIIPositive

2V:approx. 55o1 .613 t .0031 .623 + .0031 .636 + .003

Lrrnroprtrt,rrn

Lithiophilite is orthorhombic with perfect basal and good sidepinacoidal cleavage. At Buckfield it occurs as it does at Branch-

ville, in anhedrons, single individuals sometimes measuring as

much as ten centimeters across. It is pale salmon pink in color

and for the most part very fresh.Under the microscope the pleochroism usually assigned to this

mineral is lacking and it is colorless in all directions. The indices

of lithiophilite from both Buckfield and Branchville, Connecticut,the type locality, were measured. They are given below:

Buckfield (FeO:z.9aV) Branchville (FeO:12.57Vo)a L 663 + .003 1 .6241 .003p 1.666+.003 1.677 + .003t 1 .673+ .003 1 .684+ .003

The indices increase with higher percentages of iron.In composition lithiophilite is a phosphate of manganese and

lithium with but little iron. It is isomorphous with triphylite

which contains much iron and little manganese and is blue in

color. Chemical analyses were made of the lithiophitite specimens

whose indices were measured. The specimen from Branchville

was collectedin 1924 from the new openings.

20 Amblygonite is as often positive as negative, and shows a wide

indices, accor{ing to optical studies by Helge Backlund, Amblygonite

Papers of Miner. Inst., Stockholm Universit5r. Vol. I, No.4' 1918.

range ofat Uto,

IOURNAL MINERAINGICAL SOCIETY OF AMERICA

Analyses of lithiophilite by Miss Vassar.Buckfield Branchville

SiOz 0.16 per cent 0.17 Per centFeO 2.94 12.57CaO trace traceNaro 0.24 o.24HzO * 0 .65 0 ,30PeOr 44.95 45.05MnO 42.58 32'65L i ro 9 . l l 9 .23

100.63 per cent 100.21 per cent

The least FeO previously reported was 3.99 per cent' on a

difierent specimen from Branchville.2l The Buckfield material

with but 2.96 per cent FeO is the nearest of any lithiophilite so far

analyzed. to the theoretical end point of the triphylite-lithiophilite

series.At Buckfield lithiophilite occurs frozen to the pocket walls,

which generally consist of massive quartz. A change in the

character of the solutions following the deposition of lithiophilite

made this mineral unstable, and it was extensively attacked and

replaced by lat6r minerals.Beside its well known occurrence at Branchville lithiophilite

has been reported from Tubbs Farm, Norway, Maine; Faires

Mine,22 Cleveland County, North Carolina; and Pala, California.

A specimen from the latter locality in the Harvard collection shows

lithiophilite with sicklerite, a more hydrous lithium-iron-manganesephosphate.

TRrpnvrrrB

Triphylite is represented in the Buckfield collection by a single

isolated fragment measuring five by five by two and a half,centimeters, blue in color.

Owing to its chemical similarity with lithiophilite it is assumed

that triphylite belongs in Class III as well. As no other minerals

were present in the specimen its paragenesis could not be deter-

mined further. Probably a very temporary increase in the amount

of iron in the ascending solutions was responsible for the forma-

tion of a small amount of triphylite at Buckfield'Triphylite has a wider geographical range than lithiophilite'

21 Brush and Dana. Loc. cit., p. 67 .2 Graton, L. C., Gold and Tin Deposits of the Southern Appalachians, [/' S'

CeoI. Su.rv., 8u./,1.293. p. 38, 1906.

384 TH E AM EMCAN MI NEMINGIST

It has been found at Mount Mica, Stoneham, and Peru, Maine;Grafton, New Hampshire; Norwich, Massachusetts; Rabenstein,Bavaria; and Keity6, Finland. At several of these localities it isassociated with spodumene.

Rnopocnnosrrn

The rhodochrosite of Class III has the pink color typical of themineral. It appears occasiorrally in distinct, small crystals showingthe forms M (40+l),1 (0221), and a (2L3t), but most of it is inanhedral masses up to ten centimeters across. A black manganeseoxide coats much of the material.

A chemical analysis by Miss Vassar of the Buckfield rhodochro-site belonging to this generation follows:

FeO 2.97 per centCaO traceCOz 38.43MnO 58.79

100.19 per cent

This is the only appearance of a primary carbonate. For a shortperiod the proportions of COz to PzOr in the ascdnding solutionsmust have been such that the former displaced the latter as thenegative radical.

No specimens could be found containing rhodochrosite andlithiophilite adjoining, so the relative age of these two minerals isin doubt. Like lithiophilite, rhodochrosite has been partiallydissolved by subsequent solutions, and replaced and coated bylater minerals.

Rhodochrosite is rare among the pegmatites of central Maine.A small quantity was found at the Towne quarry, Auburn, andat the Berry quarry in Poland. At Branchville this mineral wascommon with the manganese phosphates found there.

Eospnonrru

The long yellow prismatic crystals of eosphorite make it themost striking mineral in Class III. A picture of a group of suchcrystals is shown on Plate B. The mineral is orthorhombic withthe direction of elongation taken as the vertical axis. The facesof the prism zorre are striated vertically. Forms and habit of thecrystals are identical with those of the type material from Branch-vil le. Connecticut.

JOURNAL MINERAINGICAL SOCIETY OF AMENCA 385

The refractive indices of this eosphorite are as follows:

a : 1 .629,0 : 1 .650, ry : 1 .658.These are slightly below those given for a higher iron variety

from Branchville.23The ideal eosphorite is a hydrous phosphate of manganese and

aluminum. It is isomorphous with childrenite, which contains

iron instead of manganese. A chemical analysis of the Buckfield

eosphorite by Miss Vassar is given below:

SiOz 0.90 per centAl:oa 22.37MnO 29.94FeO 1.38HzOt 15.34F trace

PzOr 29.89

99.82 per cent

Buckfield eosphorite follows lithiophilite in closely approaching

the theoretical end point of the series. Its content of FeO, 1.38

per cent, is much lower than that in any of the childrenite-eosphor-ite analyses published in Dana or Doelter. The Branchville eosphor-

ite contained 6.62 pet cent FeO.With the introduction of eosphorite chemically combined water

becomes important. This and the succeeding minerals in Class III

contain fair amounts of \Mater.Determination of the relative age of eosphorite is complicated

by two features of the mineral. One is its strong crystallizationpower which tends to mask its true relationship with associated

minerals. The other is its unusually high resistance to attaqking

solutions, which have in some instances removed the neighboring

minerals to such an extent that eosphorite will rest upon and

appear later than younger minerals.Although on the whole eosphorite deposition followed the

formation of rhodochrosite there was a slight overlap of the two.

This is shown on one specimen where a large crystal of eosphoritestarted to grow out from a rhodochrosite mass only to have the

Iatter add a little to its size, burying the stump end of the eosphor-

ite crystal a fraction of an inch. This and other examples of

23 Larsen, E. S., The Microscopic Determination of the Non-opaque Minerals"

U. S. Geol . Sun.,8u11.679,p.72, 1921.

386 TEE AMEKICAN MINERALOGIST

eosphorite crystals lying on and growing out from rhodochrositemasses prove the slightly later age of eosphorite.

Known localities for eosphorite outside of Buckfield are limitedto Branchville, Connecticut, and Poland,2a and Hebron, Maine.Specimens from Hebron have been called childrenite, but afteran optical study Larsen stated that the mineral was probablyeosphorite.2s Childrenite has been found at Mount Mica and atfour English localities, one in Cornwall and three in Devonshire.

Eosphorite from Mount Mica has not heretofore been described.Specimens in the Harvard laboratories contain this mineral insmall radiating needles coated by dahllite. It is embedded inmassive siderite. Under the microscope the Mount Mica eosphoriteis pale yellow green, whereas the Buckfield material is colorless.The color and slightly higher indices show that the Mount Micaeosphorite is higher in iron than that from Buckfield, but it is notchildrenite because the axial ansle for violet is sreater than thatfor red.

FelRrrrtpr:rB

Straw colored plates here and there among the Class Iff mineralswere found to consist of small crystals of fairfieldite. These aretriclinic, have one perfect cleavage, and in thin plates are ab-solgtely colorless and transparent.

Crystals of simple form were seen but proved to be too dullfor measurement. The largest crystal, shown in Plate III, A,and nearly 3 centimeters long, is entirely coated with dahllite.

Fairfieldite from the zone of oxidation is white and opaque andoften coated with manganite. The nature of the alteration maybe seen under the microscope. A white opaque mineral which maybe kaolin has commenced to attack the fairfieldite, working firstalong the cleavage cracks and from them laterally into the mineral.Sometimes a yellowish to olive green alteration product is presentbut chemical and optical tests on this mineral were hopelesslycomplicated by the unfailing presence of residual fairfieldite.

The refractive indices on the Buckfield fairfieldite were deter-m ined as f o l l ows : a :1 .633 , F :1 .641 ,1 :1 .652 .

2a Drugman, Julien, On Childrenite from Crinnis Mine Cornwall, and Eosphoritefrom Poland, Maine. Mineral.. Mag.,1915, pp. 193-201. The Poland eosphorite con-tained 5.55/p FeO and showed the same forms as are found at Buckfield.

26 Loc. cit., p. 57,

JOARNAL MINERALOGICAL SOCIETY OF AMERICA s87

Fairfieldite is a hydrous phosphate of calcium and manganese,

with iron generally replacing a little of the manganese. The iron

in the Buckfield material was very low. An analysis by Miss

Vassar follows:SiOz 1.07 per centFeO 1.00CaO 29.77HzO+ 9.94PzOa 37.79MnO 19.68

99.25 per cent

The lowest percentage of iron in previously analyzed fairfieldite

was 3.42 per cent, in a specimen from Branchville.This is the only appearance in Class III of calcium in more than

a trace. In fact, fairfieldite is one of the few minerals in the entire

suite to contain this element. The calcium that was present in the

ascending solutions during the other periods was usually taken

care of by apatite, which does not appear in Class III.Fairfieldite was deposited after eosphorite. fn some instances

eosphorite crystals cut through fairfieldite and appear later in age,

but a close examination shows that the cleavage directions in the

fairfieldite on opposite sides of the eosphorite are never parallel.

The latter does not divide single individuals, but merely lies

between separate crystals, of later age.The type locality for fairfieldite is Branchville, Connecticut.

Sandberger described an occurrence of this mineral, first under the

name of leucomanganit, at Rabenstein, Bavaria.26 Oberpfalz,

Germany, is another reported locality.

Rpnrrwcrrr

Reddingite, a rose pink to reddish brown mineral, crystallizes

in octohedroids of the orthorhombic system. It is usually granular,

and ranks with rhodochrosite as one of the iommonest minerals

in Class III. It may be distinguished from that mineral by its lack

of cleavage.The Buckfield reddingite is pleochroic. This serves to dis-

tinguish it in the thin section from lithiophilite. It also has a much

higher birefringence. The indices follow:a:1.643. X:color less.g:t.648. y:pinkish broivn.

t :L.674. Z:pale yel low.

n Jahrb. Jiir Mineralogie, p. 370, 1879, No. 1, p. 185, 1885.

388 TE E AM ERICAN MI NERALOGIST

The indices of the Branchville reddingite average .008 higher.A greater percentage of iron in the latter material probablyaccbunts for this difference.

Reddingite is a hydrous manganese phosphate, 3 MnO, P2O5,3HzO, and as in fairfieldite a small amount of iron replaces themanganese. An analysis of the Buckfield reddingite by MissVassar is given below:

Insol.(SiO) 0.30 per centFeO 2.19MeO 0.35CaO 0.73H2O+ 13.14PrOu 34.54MnO 48.15

99.40 per cent

The Branchville reddingite contained 4.70 per cent FeO.Reddingite is definitely later than all the other minerals in

Class III. Previous to its deposition the ascending waters becameactive solvents and removed in part the preceding minerals(except the extremely insoluble eosphorite) forming cavities whichlater became lined with reddingite. The mineral also replaces,as veinlets in the lithiophilite are very common.

Heretofore reddingite has been known only at Branchville,and there in very small quantities. The abundance at Buckfield ofthis rare mineral is remarkable. The very rare crystals foundwith idiomorphic form are identical in habit with the type crystalsfrom Branchville.

MINERALS OF CLASS IV

Class IV is divided into two periods of mineralization. In theearlier period veins of lepidolite were formed in the zone containingClass II minerals, while veins of rhodochrosite were formed in thezone ol Class III minerals. Both are clearly later than the samespecies with which they are thus associated. The confinement ofthese vein minerals to zones containing earlier deposits of thesame minerals suggests that they did not result from an influx ofnew material at this stage, but were formed by soltrtion andredeposition of material already in place. The waters bringing thisabout were probably hypogene as we know from the presenceof later minerals that hydrothermal activity had not yet ceased.

JOURNAL MINERALOGICAL SOCIETV OF AMEMCA 389

The later and main period of Class IV mineralization closed the i

hydrothermal activity at Buckfield. It represents a lithia-silica

phase in the ascending solutions. Cookeite, qtrartz, apatite and

herderite were deposited in the order named. The first two appear

in great abundance. The latter are of very minor importance'

These four minerals represent a well defined group' and were

deposited so closely together that they overlapped.

The vein minerals were deposited largely in fissures through

earlier minerals. Cookeite and quartz also fiIled open spaces

created by the solution of pre-existing minerals' The filling was

far from perfect, as great porosity exists in the later Class IV

specimens and in some the open spaces may be measured in inches'

Volume by volume replacement was less common and was mostly

confrned to the alteration of vein lepidolite into cookeite.

The Class IV minerals are quite evidently late in age' as shown

by the cross cutting relationship of the lepidolite and rhodochrosite

veins and. the superimposition of quartz and cookeite on the

minerals of the earlier classes. In some specimens such typical

Class II minerals as cleavelandite, lepidolite, and milky quartz

are coated by cookeite and quartz.In other cases removal of earlier minerals was far more complete'

Often only a few bits of the difficultly soluble minerals are left in

patches in quartz and cookeite as remnants of an earlier period'

Lepidotite, columbite, manganotantalite, and kaolinized spodu-

mene occur in this manner.In one specimen qtartz and apatite are replacing rhodochrosite

and amblygonite of Class IILA final phase of this sort in the deposition of pegmatite minerals

is the rule rather than the exception in central Maine. At Green-

wood it was an outstanding feature.

LrprtornB

In Class IV lepidolite occurs exclusively in veins. This habit

easily distinguishes it from the earlier hydrothermal and magmatic

types. The veins are lilac in color, and cut minerals of Class II,

especially spodumene. The separate individuals in the veins are

very minute. They vary sufficiently in orientation so the vein

has no well-defined cleavage.In the majority of cases the veins have been isolated by the

complete removal of surrounding minerals. The result is an

3m TH E AM EMCAN MIN ERAINGIST

irregular sheet of massive lepidolite ranging from paper thin up toone centimeter in thickness. These are found buried in kaolin inthe bottom of the pockets. Very often minor veins of much smallerdimension extended out from the large veins into cleavage andother cracks in the surrounding minerals. In that case a greathost of excessively thin shelves jut out from the side of thickerslabs (Plate III, B). Their rough parallelism suggests that theywere formerly veins extending into a highly cleavable or platymineral, such as cleavelandite.

One specimen contains as remnants of Class fI mineralizationa few quartz crystals and many small books of lepidolite. Thelatter are connected to each other by paper thin isolated veins oflepidolite. The plane of the vein is at right angles to the plane ofthe basal cleavage in the book lepidolite. Larger veins cut acrossthe specimen in a few places. These likewise have a multitude ofsmaller offshoots. The secondary veins all have the same gbneralstrike, although often joining or diverging down the dip. No traceof the mineral or minerals serving as host for this depositionremains.

RuooocuRosrrnSmall veins of rhodochrosite cut through the minerals of Class

III. These are obviously later than the massive rhodochrosite andphosphate minerals of that class. In many instances the earlierminerals have been removed by solution and dike-like forms are theresult. These isolated veins are roughly parallel to each otherexcept for an occasional vein which intersects the others at a lowangle.

Deposition of rhodochrosite continued during the period ofsolution of the neighboring minerals and as a result the projectingveins are lined with small pink rhodochrosite crystals, showingthat ascending hot waters dissolved and redeposited rhodochrositeover a relatively long period.

CoorprrB2TCookeite is an abundant and rather conspicuous mineral at

Buckfield. Large specimens were obtained coated with brownishaggregates of plates shown schematically in Fig. 2. The substanceis so soft that the slightest touch broke the edges of these platesleaving a light yellow mark very much as the hand leaves a mark

27 Optical data and sketches of cookeite by R. W. Goranson.

JOURNAL MINERAI,AGICAL SOCIETY OF AMERICA 391

when it touches the bloom of a plum. The color also varies to palegreen and pink. It may readily be distinguished from lepidoliteby lower refractive indices and positive optical character. Underthe microscope the plates of cookeite appear hexagonal as in Fig. 3.Some of the plates have a uniaxial center, e.g., BEFGHK, butothers lack this central core. The uniaxial character is probablydue to the aggregate effect of three plates at 60o to ea,ch other, theaxial angle being largest midway in each segment. For example,in the segment ACEB the axial angle is largest at D with the planeof the optic axisparallel to the side AC;approaching,4 the anglegets smaller until on the line AB the axial angle is 0, then swings60o and becomes parallel to AM, enlarging until it reaches theposition Z. The segments are striated perpendicular to their outeredges. The axial angle reaches a maximum of about 80 degrees.

Some of the plates have narrow rims which are dark colored andmay be due to an alteration of cookeite. One of these borders waslarge enough to note that the index was slightly less than the indexof the cookeite.

Frc.2 Cookeite.

The indices of cookeite, determined by daylight, are; a:1.576*.003; F:1.579+.003 (seems to be constant in value) ;^y:1.597+.005.

The cookeite was separated by heavy solutions for analysis.The specific gravity of the clean sample was then determined bythe pycnometer as 2.670; (according to Brush the sp. g. is 2.70,according to Penfield 2.675).

Chemically cookeite is very similar to Iepidolite. The chiefdifferences are a greater percentage of water and correspondingly

TH E AM ERICAN MI NERALOGI ST

Frc, 3. Basal plate of cookeite showing optical observations and pseudo-hexagonal habit.

smaller amounts of fluorine and potash in cookeite. An analysis ofBuckfield cookeite by Miss Vassar follows:

SiOz 34.81 per centAlzog 45.90FesOs 0.72CaO traceNazO\ n q?KrO JH:O* 14.87F 0 . 1 3MnO traceLrzO 3.59

100.54 per cent

The green cookeite often occurs lining solution cavities and

cleavage faces in microcline. Later quartz crystals rest upon the

cookeite. Plate I, A pictures a cavity coated in this manner.

Solution and removal of microcline coated by quartz andcookeite

may leave behind a mass of empty shells. Plates IV, A, and IV,Billustrate two stages in this process. Lepidolite, cleavelandite,

and early hydrothermal. quartz minerals of Class If are all coatedlocally with a later incrustation of cookeite. In one specimen

cookeite had replaced spodumene, preserving the structure of that

mineral.

JOURNAL MINERALOGICAL SOCIETY OF AMEKICA 393

A great deal of cookeite is disseminated through and intergrown

with the quartz of Class IV. - Here it is usually pink or yellow,

sometimes cream colored. It is on the whole earlier than the

quartz, and appears to be undergoing replacement by quaftz in a

few places.One other occurrence of cookeite was observed at Buckfield. In

this the isolated veins of lepidolite previously described have been

partially altered into cookeite. Sometimes the secondary veins

are completely altered, while the outer edges only of the main

vein will be changed from lepidolite to cookeite' This is alteration

in situ, cookeite resulting from hydration of lepidolite.

Cookeite is usually considered an alteration product of either

tourmaline or lepidolite. Examples of the alteration of tourmaline

into cookeite are rare at Buckfield, but this change is well shown

in specimens from Hebron and Mount Mica. Alteration, or

hydration, of lepidolite into cookeite has just been described'

But there is much cookeite at Buckfield and elsewhere in central

Maine that cannot be accounted for by either of these processes'

Bastin2s says, in referring to cookeite: "Abundant as a coating in

most of the pockets in the coarser pegmatites' Not an original con-

stituent, but secondary and due to water deposition." But, much

of the Buckfield cookeite is definitely earlier than the abundant and

intimately associated qvartz, which is in turn eaiTier than apdtite

and herderite. It would seem then that this cookeite is of hydro-

thermal origin. The low temperatures prevailing during this final

period of hypogene deposition permitted the formation of cookeite

rather than the less hvdrous lepidolite.

qoo*",

Quartz is the commonest mineral in Class IV. Some large

masses resulting from this period of deposition consist of over

ninety percent qtf,attz. The crystals themselves are small, never

exceeding two and a haif centimeters in length. They are clear

and absolutely colorless. Even the most massive specimens are

extremely porous, as the crystals do not fit together very closely.

These Iarge quartz aggregates, consisting of a multitude of small

individuals, are pink and yellowish in color, due to the presence of

flakes of cookeite throughout the mass.

zs Bastin, E. S., Geology of the pegmatites and associated rocks of MaineU. S. Geol. Sun., Bu'Ll. 445, p. 16, 1911.

394 THE AMEMCAN MINERALOGIST

The clear and colorless character and the small size of the quartzcrystals usually distinguish them from those belonging in Class II.The latter are more often milky than colorless. When they arecolorless distinction must be made on a basis of association. Thepractically invariable presence of cookeite is a good criterion oflater age.

Sometimes the q.uartz crystals of Class IV project in parallelgroups, from thin shelves. The latter are likewise parallel to eachother and are usually composed of finer grained qtrartz. They mayalso contain cookeite, especially toward the center of the slab.

Specimens illustrating this structure represent the last of asequence of interesting events. In the first place a pocket wasformed containing the typical minerals of Class II, such as lepi-dolite and cleavelandite. Further hydrothermal activity broughtabout the formation of lepidolite veins, connecting the lepidolitebooks. The roughly parallel structure of these veins may havebeen due to the platy character of minerals traversed, such ascleavelandite. Whatever the host it was soon removed by thedissolving activities of the ascending solutions. Lower tempera-tures and quantities of water brought about the hydration of thevein lepidolite into cookeite. Then silicification became dominantand the cookeite was partially or wholly replaced by quartz. Fromlepidolite to cookeite to quartz, then, is the history of some of theseveins. During and after their last replacement they served as abase for many quartz crystals growing Iaterally into the openspaces between the shelves.

$ilicification as a final stage in pegmatite mineralization had amuch greater development at Greenwood, and has been notedas an important phase at Auburn.

AparrrBApatite is unimportant among the minerals of Class IV at

Buckfield. It is very clear, and pale green or light blue in color.Crystals are characteristically tabular parallel to the base, andshow the forms zz(1010), r (1011), r (1012) and s(1121).

Class IV apatite is distinguished from earlier types by its habitand associations. It commonly lines cavities in the cookeite-quartzaggregates and where these cavities are tabular in shape the crustson the opposite walls meet and simulate a vein. The pegmatitesat Mount Apatite and Greenwood have produced many beautifulspecimens containing apatite of this type.

JOURNAL MINERALOGICAL SOCIETY OF AMEMCA 395

He nrrnrrB

But few herderite crystals were found associated with the ClassIV minerals. These were small, light brown, and clear. The herder-ite of Class II was translucent rather than transparent.

Where found herderite was always associated with apatite in

small openings in the cookeite-quartz masses.

MINERALS OF CLASS V

Most of the minerals in the last group occur as bristles, stalac-tites, crusts, or f i lms associated with open spaces. They arewithout doubt secondary as in every case they consist of elementsobtainable very near at hand and their method of deposition istypical of minerals formed by ground water activity. Many of the J

minerals themselves are characteristic of supergene deposition.Due to their secondary origin these minerals are found scattered

throughout the pegmatite wherever the parent primary mineralsare intersected by the zone ol oxidation. Thus certain amounts of

kaolin may be found where microcline, belonging to Class I, Iiesclose to the surface. Kaolin also results from the decompositionof spodumene, a Class II mineral. Cleavelandite, of the sameclass, is prone to alter into montmorillonite under near-surfaceconditions at Buckfield. The greatest variety of secondaryminerals is found where the Class III minerals reach the zone of'

oxidation. The presence in the primary minerals of this class ofMnO, PzOs and COz has been responsible for the formation of

psilomelane, manganite, an unknown manganese phosphate,

rhodochrosite, and dahllite.Owing to the scattered positions in the pegmatite of the secbHd-

ary products no sequence of mineralization can be applied to the

class as a whole. It is probable that more than one mineral was

being deposited in different places at one time. A fairly definite

sequence for the Class III secondary products is possible, however'

Several specimens show psilomelane altering into manganite.Likewise manganite alters to an unknown manganese phosphate.

Rhodochrosite is later than manganite, but dahllite was formed

before it ' KeorrN

A surprisingly small amount of the Buckfield feldspar is kaolin-

ized. But spodumene was very susceptible to this alteration and

fresh pieces of spodumene are rare. Many more specimens are

396 THE AMEMCAN MI NEKALOGIST

found in which this mineral has been completely kaolinized.Usually the original structures of the spodumene are preserved,giving a true pseudomorph of kaolin after spodumene. Lepidoliteveins formerly cutting spodumene crystals are found buried in amass of kaolin in the pocket debris.

Other minerals sometimes incipiently altered to kaolin areamblygonite, fairfieldite, cleavelandite, and topaz.

MoNruonrr,LoNrrE

Cleavelandite in the zone of oxidation is sometimes foundpartially altered to a pink, clay-like substance. This is one of theclay minerals, known as montmorillonite. The bright pink colorof the fresh material pales upon exposure, probably due to partial

dehydration.Under the microscope this material is seen to consist of an

irregular aggregate of small scales or plates. The mineral iscolorless in very thin plates, but becomes pink and opaque with anincrease in thickness. Optical data are: Biaxial negative, 2V:a lmost 0, 0: 1.513.

Montmorillonite is a very indefinite species. The optical dataabove more nearly coincide with those given for leverrierite,2eanother hydrous aluminum silicate.

PsrrouBleNo

Hard, black botryoidal crusts coating rhodochrosite proved tobe psilomelane. This mineral is limited in its occurrence to thezone of weathering and even there it is quite subordinate tomanganite, with which it is associated. The primary mineralfrom which psilomelane was derived was usually rhodochrosite.

MeNcaNrrr

Manganite is one of the commonest of the secondary minerals.It is widespread in the surface zone, even forming a fine film onquartz and cleavelandite. Thickpr deposits are found on theminerals actually undergoing alteration, such as rhodochrositeand lithiophilite. In a very few specimens manganite coatedpsilomelane, preserving the botryoidal character of that mineral.In this case it was quite evidently derived from psilomelane, butit is very doubtful that all the manganite passed through a

2e Larsen, E. S., The microscopic determination of the non-opaque minerals,

U. S. Geol. Sura., Bull..679, p,245, 1921.

IOURNAL MINERALOGICAL SOCIETV OF AMEEICA 397

psilomelane stage. In one instance the alteration about the edgesof dahllite into manganite was observed.

Rpo MaNcaNESE PHos?HATE

fn a few specimens botryoidal surfaces of manganite (pseudo-

morphous after psilomelane) were coated by a thin, velvety, brickred crust. The Iatter very evidently resulted from alteration ofthe manganite, as the radiating fibers forming the rounded surfaceare red on that surface, but darken toward the interior, where theybecome indistinguishable from the black .manganite.

The fibers are extremely fine, and so soft and brittle that theypowder immediately when an attempt is made to work with thematerial. The quantity present was insufficient for a chemicalanalysis. A bead test proved the presence of manganese, also aphosphate reaction was obtained with ammonium molybdate.

Microscopic examination was hindered by the small size of

the particles and their platy character. The mineral is biaxial andprobably negative. The plates due to a good cleavage are perpen-

dicular to X. Further optical data follow:

a: | .71 , 2V: la rge ;9 : r . 7 3 ,7 : 1 . t + ,

Y:yellowish brownlZ:deep red brown.

It was at first thought that the mineral might be sicklerite, a

hydrous lithium manganese phosphate. The indices of both lie

between t.7l and, 1.75. Likewise, the pleochroism is somewhat

similar for both. But comparison with the type sicklerite from

Pala, California, brought out the following difierences: 1. Bire-

fringence greater for sicklerite. 2. Sicklerite gives good lithium

flame, while unknown gives none. 3. Sicklerite readily soluble in

nitric acid. Unknown but difficultly soluble. 4. Sicklerite is much

harder.RuooocuRosrrB

Ground water activity at Buckfield produced a third generation

of rhodochrosite. In Class III this mineral appeared in masses,

in Class IV in veins and druses, and in Class V in minute bristles

or quills projecting out from the surfaces of earlier minerals.

These much elongated crystals vary in color from white to brightyellow. A few may be seen in Plate II, B.

The c-ommonest primary minerals coated are rhodochrosite and

reddingite. One small crystal of rhodochrosite has a pompadour

398 TEE AMEMCAN MINERALOGIST

of white secondary bristles. These project upward from about thetop of a steep rhombohedron on the primary crystal. The secon-dary rhodochrosite fibres are parallel in crystallographic orientationto the host.

These white or yellow quills of rhodochrosite are without doubtsupergene in origin. They were deposited even after the man-ganite. In one specimen a somewhat spherical mass of manganiteis covered with secondarvrhodochrosite fibers like spines on a burr.

. Denrr-rrr

Dahllite, a calcium phosphate-carbonate, appears in yellowishgreen crusts coating various minerals of Class III. The coating is

most striking when eosphorite is the host. Prismatic crystals of

that mineral are often completely covered and the terminationsrounded off, so that pseudostalactites result. Solution remnants offairfieldite and rhodochrosite are similarly coated by crusts ol

dahllite. These may be seen on Plate III, A.

Under the microscope the yellgwish green crusts are seen to

consist of parallel fibers normal to the surface. The mineral is

uniaxial and negative, and the optical properties of the Buckfieldmaterial checked up quite closely with published data on dahllite.30

A minor occurrence of dahllite was noted in some of the rhodo-

chrosite specimens. Instead of well-defined fibers dahllite here

appeared in excessively minute yellowish particles replacing

rhodochrosite. The fibrous dahllite seems to be merely a crust,

resulting from ground water deposition on any handy mineral.

On the other hand some dahll ite replaced rhodochrosite, but

without the production of fibers. At Mt. Mica dahllite was also

observed as a dark green coating on eosphorite. The prismatic

habit of the latter mineral produces pseudostalactites of dahllite

similar to those at Buckfield.

Certain specimens from Auburn in the Harvard mineralogical

laboratories contained a mineral in small but well defined white

rosettes which coated earlier minerals. Optical and chemical

study proved the unknown to be francolite, a carbono-phosphateof calcium which is chemically very similar to dahllite, but containsfluorine and differs from that mineral in being biaxial'.

30 Larsen, E.5. , Loc. c i t . , p. 196.

TOURNAL MINERALOGICAL SOCIETY OF AMERICA 399

GREENWOOD

The Greenwood deposit is located well up on the western flank

of Noyes Mountain. A zigzag trail makes the steep ascent from

valley to quarry floor. The slope of the ground is such that waste

material which has been thrown over the dump is strewn down

several hundred feet of mountain side.

The country rock in which the pegmatite is intruded is a mottled

green gneiss. The individual grains are small but the gneissic

bands themselves are wide. The green color is due to the prepon-

derance of pyroxene. Other important minerals visible in the thin

section are chlorite, qtrarLz, and oligoclase.

The pegmatite dike cuts across the bands of the gneiss' Its

outcrop runs along the brow of the hill for many yards, strikes

N 60 W, and dips very steeply into the hill. The outcrop averages

ten feet in width, but in one place it is much wider' Here an

ofi.shoot of the main vein into the gneiss produces a total width for

the pegmatite of about thirty feet over a short distance'

The quarrying operations were mostly confined to this local

to fifteen feet at the floor.Two types of texture in the Greenwood pegmatite are very

apparent. Away from the swelling the minerals, although coarse'

ti" tigntty intergrown. Specimens from these parts are massive'

with no open spaces visible. On the other hand the portions of the

pegmatite wiihin and neighboring the offshoot are extremely

poiorrr. Pockets u.. .o*-on and where these are lacking the

4OO THE AMEKICAN MINERALOGIST

The solidification of the pegmatite magma produced one group ofminerals. Here occur feldspar, quartz, and other minerals makingup the main mass of the pegmatite.

As at Buckfield, l iquids discharged during the crystall ization ofsuccessively lower portions of the magma flowed upward, dissolv-ing and depositing as they did so. They did not confine themselvesto the outl ines of the original pegmatite but extended theiractivity out into the gneissic country rock. This produced thebulge or swelling in the dike previously described.

But two phases in hydrothermal activity may be recognizecat Greenwood. The first of these was exactly the same as at Buck-f ie ld. This was a s i l ica-sodium-rare e lement phase, producing suchminerals as qtartz, cleavelandite, Iepidolite, tourmaline, caesiumberyl, etc. Buckfield's Class III, resulting from a l ithium-manganese-phosphorus phase, is lacking. Not a mineral of thatsuite, with the exception of amblygonite, has been found atGreenwood. The fourth class, however, was extraordinarily welldeveloped here. At Buckfield this was a l ithium-sil ica phase.At Greenwood phosphorus must be added to the l ist, for apatiteis present in abundance along with cookeite and quartz.

Supergene activity produced but few minerals. The mostinteresting of these is kaolin formed from amblygonite in nodules.

N{aclrlrrc Pn.A,sB

The magmatic phase of the Greenwood pegmatite producedmuch the same mineral association as at Buckfield.. The majorconstituents are white and pink microcline in anhedrons under ameter across and gray to colorless quartz. Large books of musco-vite up to sixty centimeters across and a centimeter thick arecommon at Greenwood but were not found at Buckfield. Trans-parent to opaque green beryls are found but are less abundant thanat Buckfield. The largest crystal found in 1923 was fourteencentimeters across and ten long. Black tourmaline and dark greenmanganapatite are similar in character and occurrence to thoseat Buckfield. Small red garnets are concentrated in layers parallelto the walls of the pegmatite as they commonly are in other suchdeposits. A thick layer is next the footwall; a thinner layer belowthe hanging wall has garnet, black tourmaline and microcline.Arsenopyrite in widely scattered small anhedrons is rare.

JOURNAL MINEKALOGICAL SOCIETY OF A],TERICA 401

Frnsr HyorcrHERMAL Pnasp

The magmatic phase was succeeded by two hydrothermal phases.The first of these was characterized by large amounts of silica,resulting in the formation of many quartz crystals; sodium, whichcombined with silica and aluminum to form albite; and severalrare elements such as glucinum, boron, caesium, l ithium, colum-bium, which entered into a variety of minerals.

As at Buckfield cavities were formed by dissolving activity onthe part of the ascending solutions. One pocket was three meterslong and several pockets a third of a meter to a meter in diameterwere found. Many of the cavities were completely l ined withhydrothermal minerals, in others massive qtartz formed a partof the wall.

Very little difference exists between Greenwood and Buckfieldin regard to the minerals produced during this period. At bothlocalit ies quartz, cleavelandite, and lepidolite predominate overthe other minerals of this class. Of the minor minerals tourmalineand spodumene were more abundant at Greenwood than atBuckfield. On the other hand some of the rarer minerals atBuckfield do not appear at Greenwood.

QuenrzA great variety oI quartz crystals, and some magnificent speci-

mens, have been quarried at Greenwood. These have been foundeither l ining the cavity walls or loose in the pocket sand. Crystalsvary in length from one to thirty centimeters. The large crystalsare usually milky, the smaller ones clear or smoky. Many smallpockets were barren save for one or two small clear or smoky qtartzcrystals. In the larger pockets groups were the rule. Some of theseconsist of several odd sized crystals in irregular orientation.Others, of truly spectacular appearance, consist of a parallelaggregate of smoky or milky qlarLz crystals (Plate VII, B).Besides the uniform orientation, these individual crystals areremarkably consistent in size. They vary from one to four centi-meters in length, over an entire specimen, but any two adjacentcrystals are usually quite similar in size. These parallel groupsmay be frozen on to massive quartz of the pocket wall, or theymay cluster on a single large quartz crystal. In the latter casecrystallographic directions in the individuals of the aggregate areparallel to similar directions in the host. In some instances the

n2 TE E AMEMCAN MINERALOGIST'

large crystal is incompletely developed on one side, and a multitudeof smaller crystals have so arranged themselves as to tend to

complete the crystal form.The separate crystals in a cluster usually merge together on

prism faces. Sometimes the groups are tabular, due to addition in

one plane only. At other times growth has been in all directions,

and striking turret-like forms are the result.There is some evidence that the earlier crystals to form were

milky in color, and the later ones smoky. In some instances

smoky crystals give way to milky crystals as one penetrates into

the cluster. One slab two feet long is covered by a host of small

parallel quartz crystals. Those on the outside are smoky, but

farther in they become milky.The ascending solution deposited qlrarLz over rather a long period

as shown by the succession of clusters on many specimens.

Ornnn MrNrners

The cleavelandite at Greenwood does not difier from that found

at Buckfield. It is typical of early hydrothermal activity at both

localities. Large masses were found in and about the pockets in the

pegmatite.Lepidolite was formed during one period only at Greenwood'

Here it occurs either in beautiful lilac colored books up to one

centimeter wide and an equal thickness, or in massive aggregates

of fine plates, Iavender, white, or even pale green in color. Some of

these aggregates were thirty centimeters or more through. Both

types of lepidolite are commonly associated with cleavelandite.

Tourmaline likewise has two modes of occurrence. It is some-

times found in green crystals radiating rather irregularly from the

pockets. Although fairly clear these crystals are never gem

worthy. Most of the individuals are from five to eight centimeters

long, but an occasional one is twice that length. Later silicification

has in most cases partially destroyed the crystals' In the second

occurrence tourmaline appears in green transparent crystals.

When found these are usually loose in the pocket sand. Some

are doubly terminated and thinner than a needle. As at Buck-

field many of the pocket tourmalines are gem worthy.The largest specimen of spodumene collected at Greenwood is

fifteen centimeters wide and thirty long and this is but a fragment

of a larger piece. The mineral is decidedly replacive, exhibiting an

JOURNAL MINERALOGICAL SOCIETY OF AMEMCA 4fr3

irregular contact toward the older magmatic minerals. It is palegreen, and some pieces are translucent. Kaolinization is incipientonly.

Amblygonite occurs in very striking forms. One crystal foundby Mr. Noyes and shown in Frc. 4 is a complete individual 15 cm.long, 8 wide and 5 thick. It is flattened parallel to the domeh(l}l) and shows the forms c(001), o(100) , z(120), Z(101), and

e(021). Most of the amblygonite however occupies the centers of

Frc. 4. Amblygonite crystal.

nodules composed of alteration products in concentric arrange'

ment. Six or more of these remarkable specimens were obtained,

the largest an oval mass about fifteen centimeters in diameter.

Some of them were completely altered to kaolin or sericite and are

described in detail on a later page. Others show a core of fresh

glassy amblygonite with polysynthetic twinning. The boundary

of the amblygonite towards the crust is irregular but the bands of

the crust are sharp and smooth. each a few millimeters thick and

variously colored dull green, brown and white. The nodules are

either embedded in lepidolite and cleavelandite or in a mass of

pure white plastic kaolin. Plates V, A and V, B show two of these

nodules, one having been sawed through the center to reveal its

structure.Cassiterite was found sparingly, in part in irregular masses or

stout pyramidal crystals embedded in cleavelandite, in part in

crystals of unusual form attached to a surface of cleavelanditeplates. One of these crystals is shown in Frc. 5 and is remarkable

in showing practically only a ditetragonal pyramid as its bounding

form, doubly terminated and as symmetrically developed as a

THE AMERICAN MINERALOGIST

model. The largest of these crystals was not more than four mill i-meters across. The same rare form, p, (i 66) is shown in a somewhatsimilar f igure by Jeremejew, of cassiterite from Siberia reproducedin Goldschmidt Atlas der Krystallformen Vol. IX, plate 89,f igwe227.

Frc. 5. Cassiterite

Other minerals of the pocket zone at Greenwood are pale greento colorless beryl, mostly deeply etched, rare embedded crystals ofdark green gahnite or zinc spinel, columbite in masses up to acentimeter across, and herderite, bertrandite and hamlinite, thelast three in minute amount only, in implanted crystals.

SBcoNo HylnoruBnuar, Pn;lsB

The second and last hydrothermal phase was characterized byenormous amounts of sil ica, with smaller amounts of l i thium andphosphorus. As a result quartz is the outstanding mineral.Cookeite and apatite are common, but are quite subordinatequantitatively. The minerals resulting from this period of activityare confined to the swell ing in the pegmatite, and in many portionsof this zone their deposition has been accompanied by the absoluteobliteration of earlier minerals. Cookeite was deposited withquartz, but apatite is distinctly later. Its single crystals anddruses rest upon quartz and cookeite.

Quanrz -a.Np Coorr,rrrMany of the quartz-cookeite specimens from Greenwood are

indistinguishable from those found at Buckfield. The quartzcrystals are small and colorless or milky. Cookeite appears inscales and flakes disseminated through the quartz aggregates. ftvaries in color from white to pink.

JOURNAL MINERALOGICAL SOCIETY OF AMERICA 405

The first quartz to be deposited formed as druses on pre-existingminerals. If crystals were available these were completely coatedby a layer of small remarkably uniform quartz crystals. At othertimes this coating was deposited on mineral aggregates, or as alining on the walls of solution cavities. Deposition was accom-panied and followed by intense dissolving activity. fn every casethe material coated was removed. If the host was an euhedralcrystal the coating retained the outline of that crystal. Some-times, instead of being coated, the original mineral was completelyreplaced by fine grained qtartz and cookeite. These two types ofpseudomorphs are described and discussed under a separateheading. But, if the host was an ill-defined aggregate merely anirregular crust resulted from its removal. Many'specimens of bothpseudomorphs and crusts were found in the cavity zone of thepegmatite.

Quartz and cookeite continued to be deposited after much ofthe pre-existing material had been dissolved and removed. Havinga great abundance of space at its disposal this q:uartz merely piledup on itself, i ts individuals assuming litt le or no similarity inorientation. It is this type of aggregate that gives certain portionsof the pegmatite their high porosity.

Quanrz PsBulolroRpns

CuenrBs Per-RcnB aNo K. K. LeNnes

The quartz pseudomorphs taken from the Greenwood ledgein numerous specimens by Mr. Noyes when the large pockets werefirst opened are among the most interesting minerals which ityielded. They are of two types and both were described byWarren,3l the one as a pseudomorph after phenacite, the other asafter topaz. It was largely in the hope of solving the riddle of theirnature that ownership of the Greenwood ledge was secured for theHarvard Museum and the later excavation there carried on.Many new specimens of both types were then secured but noneapproaching the beauty of the early groups; nor was the hope offinally determining their nature fulfilled although a new interpre-tation is offered on a later page.

According to Mr. Noyes the large pocket (see pages 363 and 400)was completely encrusted either with quartz crystals or with the

sl Warren, C. H. Mineralogical Notes. Am. J Sci., r'ol.6, 119, 1898.

406 .TEE AMEKICAN MINEM,LOGIST

hollow pseudomorphs or both. He saved many single specimensand large slabs showing groups such as are reproduced in Plate VI.During our quarrying hundreds of specimens showing broken orimperfect pseudomorphs of the same kind were thrown over thedump. They vary in size from a centimeter or less in diameter tomore than half a meter. Whatever the primary mineral may havebeen it was certainly developed in very great abundance in all thecavernous parts of the ledge. Of the embedded, solid pseudomorphsonly a few have been found. The largest, described by Warren andnow in the Harvard collection, has a diameter of about thirtycentimeters and weighs twenty-eight pounds.

The two types of quartz pseudomorphs, one due to replacementand the other to incrustation, also difier from each other crystallo-graphically. Two minerals, then, played the part of host. Notraces other than external form remain of either of these originalminerals, but some of the pseudomorphs contain cleavelandite,which was evidently replacing the missing minerals. Both types ofpseudomorph have been found on the same specimen. It is evidentthat the original minerals were associatdd together and precededcleavelandite in formation. However, their euhedral form andaggregate arrangement point toward deposition in open spaces,rather than crystallization from the primary pegmatite magma.The cqnclusion is that the original minerals of the pseudomorphswere deposited rather early during the first hydrothermal period.

Examples of the replacement type of pseudomorph are shown inPlate VI, A and wil l be described first. These are composed of f inegrained qtartz and cookeite with an occasional remnant ofcleavelandite. Crystal faces are plentiful and definite. Fivespecimens of this type of pseudomorph have been found, and thesame groups of faces occupy each.

The form is a cube, with each corner truncated by three facesof the trapezohedron (211). The angles check as closely as could be

Contact Measurements of Quartz Pseudomorphs.

Measured Theory for Warrenisometric crystal

90"+30' 900350130' 35'16',34" +60', 33"33rh'49o 48'71%',62" 600

001 to 100001 to 112ll2 to 121ll2 to ILZll2 to 2Il

92"33"36"500600

JOURNAL MINERALOGICAL SOCIETY OF AMERICA N7

expected rilhen one considers the rough surfaces involved. The

maximum error is about two degrees. When the form is set up

correctly its character is unescapable.The smallest cube among these pseudomorphs is two inches,

the largest is nine. The latter specimen contained three of these

nine-inch cube faces, with the corner formed by their junction

truncated by three smaller trapezohedron faces. Other trapezo-

hedron faces marked other corners.Under the impression that the form was rhombohedral Warren32

described the original mineral as phenacite, but the definite iso-

metric character of the pseudomorph rules out this mineral.

The most plausible guess as to the original mineral is analcite.

This is supported by the following facts:1. It is the only known mineral of exactly similar habit' One

crystal of analcite in the Holden collection from the Tyrol is a

perfect model of the pseudomorph. On page 596 of Dana's System

of Mineralogy a drawing of an analcite crystal (Fig. 3) from the

Cyclopean Islands (near Catania, Sicily), could just as well be

Iabelled a pseudomorph from Greenwood.2. The original mineral was deposited during the first hydro-

thermal period when we know the solutions were sodic.

3. Although hyd,rous and. a zeolite, analcite is known elsewhere

as bn igneous mineral, so temperature considerations cannot rule

it out here.Points unfavorable to the analcite hypothesis are:

1. The large size of the pseudomorphs. Nine inch cubes as

opposed to three inch crystals from the Tyrol.2. Analcite is more often associated with rocks of intermediate

or basic character.No other possibil i t ies suggest themselves; the cube precludes

garnet, the trapezohedron precludes fluorite.The second type of pseudomorph resulted from incrustation by

drusy quartz, followed by the solution and removal of the host'

Pictures of this type are given on Plate VI, B. Some arehollow,

others are partially filled with later quartz or earlier clevelandite.

32 Loc. cil'., p. 120. Warren's figure (idealized for phenacite) may be found also

in Appendix I, Dana, System of Mineralogy, p. 53. According to ourinterpretation

the faccs lettered p are the cuhe faces; all the others are faces of the trapezohedron.

The rhombohedral aspect of the crystal is due to setting up the cube with a diagonal

as vertical axis.

403 THE AMERICAN IIINERALOGIST

The form is prismatic, terminated bluntly by faces at ninetydegrees to the axis of elongation. The end faces, giving the cross-section of the form, are sometimes diamond shaped, at other timessix-sided. The apparent orthohombic symmetry in many of theforms suggested to Warren that the original mineral was topaz.33

Other specimens, however, appear to have but one plane ofsymmetry, and that at right angles to the axis of elongation. Ifthat is true the pseudomorphs are monoclinic, and consist of sidepinacoid, base, and positive and negative orthodome.

Attempted measurements of the angles produce a variety ofresults. Contact methods only are available and any respectabledegree of accuracy is prevented by the extremely rough nature ofthe surfaces involved. However, even with the eye, a rather widedivergence of angles may be noted. The acute angles about theend faces of the different pseudomorphs vary between 28o and 57o.Any theory as to the original mineral wil l have to allow for thiswide variation.

The suggestion is made that the host for the incrustation washeulandite, elongated parallel to the b axis. Arguments in favorare:

1. Crystallographic similarit ies. The side pinacoid, base, andpositive and negative orthodomes are very important forms inboth" fn some of the best developed pseudomorphs the anglesmatch very closely with those given for heulandite which is oftenpseudo-orthorhombic in form. Oscil latory combination of ortho-dome f aces known on heulandite would well account for the varietyof angles in the pseudomorphs. Furthermore the inside of the crustis often striated parallel to b, as it would be if the crystal faces onwhich deposition took place were so striated.

2. The close association with another zeolite, analcite.Unfavorable points are:1. Large size of pseudomorphs. The side pinacoids on the

largest specimens measure five to ten centimeters, and the b axisis 15 centimeters in length.

2. Elongation parallel to 6 is an unusual habit for heulandite.3. This mineral occurs more commonly associated with less

acidic rocks.Another possibil i ty is bertrandite, a hydrous beryll ium sil icate

which is found associated with beryl in pegmatites. Its crystal33 Loc. cit., p. 721.

JOURNAL MINERALOGICAL SOCIETY OF AMERICA 40)

form is somewhat similar, but its individuals are usually veryminute. Sti l l a third possibil i ty is feldspar, in elongated crystalswith side pinacoid, base, and negative orthodomes.sa

AperrrB

The apatite crystals are purple and clear. They appear eitherin large isolated crystals or in druses, composed of much smallerindividuals. The largest of the isolated apatite crystals measuretwo centimeters in diameter and a l itt le less in length, but themost are only about half this dimension. They appear scatteredthrough the quartz-cookeite masses, but always resting on, ratherthan embedded in, these minerals. Two or three such crystals,purple and clear, nested in a small vug walled by scores of trans-parent quartz crystals, make a very pretty picture.

But the most spectacular occurrence of apatite at Greenwoodwas as a drusy l ining on the walls of pockets. The largest pocketso Iined was pod-shaped, forty centimeters long and averaged sevencentimeters in width. A cavity of similar shape but only fifteencentimeters long adjoined. Nearby were sti l l other pockets of moreirregular shape, but l ikewise l ined with drusy crystals of apatite.The pockets of the latter type are very obviously solution cavitiesin fresh microcline. One of these is shown on Plate VII, A.

The pocket walls which are l ined with apatite present a raresight. They appear as a continuous purple mass, sparkling from ahundred points, as the individual crystals of the druse catch thelight and flash it back.

SupsncnNn Pnesn

The ground water solutions at Greenwood had litt le to work onthat 'was susceptible to their activity. No suite of fairly soluble

u Since writing this discussion of the original nature of these pseudomorphs asuggestion has been made by Dr. W. F. Schaller which should be recorded here. Hepointed out that pollucite was an isometric mineral not considered in the discussionand very likely to have occurred in the pegmatite. It has been found in greatabundance in a neighboring pegmatite in Buckfield, (Dudley's Ledge) although notin crystals. Dana records the occurrence of crystals in the Elba pegmatites withthe same forms, o, (100) and n, (211) as are present on the psuedomorphs but asthese have never been figured, the habit is not known. ft is obvious that polluciteis a much more likely minera to have been formed in this pegmatite than analcite.The writers also desire to place more emphasis on the possibility that the ortho-rhombic or monoclinic pseudornorphs might have been bertrandite. This mineralhas never been found in crystals of more than a fraction of an inch in diameter butsize is the most variable element of the pegmatite minerals.

410 THE AMEMCAN MINERALOGIST

manganese phosphates was present to give a wide range of secon-dary products as at Buckfield. Supergene mineralization waspractically confined to the kaolinization of feldspar and ambly-gonite.

fn the case of feldspar the masses of that mineral near thesurface, or adjacent to the highly porous portions of the pegmatite,have been altered to some degree. At t imes montmoril loniteresulted from this decomposition.

The nodules of amblygonite appear to have been converted intokaolin by concentric zones working inward. In the nodules pictured(Plate V) the outer crusts are kaolin and sericite, but the corehas not as yet succumbed to this alteration. In other instancesthe center of the nodule is white and compact, with a conchoidalfracture. Here kaolinization has been more complete. A greencrust also surrounds the kaolin core. Analyses by Miss Vassarof the green crust and the white core follow:

Green crust White core

SiOr 35.39 per cent 43.89 per centAlgo: 47 .o0 38.74FerO: 0 .16 0 .48FeO 0 .36 0 .06MsO 0 .10 0 .09CaO 0 .03 0.16N a s O 0 . 1 9 0 . 1 9KrO 0 .26 7 .O4HrO+ 13.63 7 .35HzO- 0 .48 1 .62P r O ; 0 . 1 0 0 . 0 6L i ro 2 .64 0 .67F 0 . 1 5 0 . 0 9

Amblygonite,Mt. Mica(Dana)

33.68 per cent

0 .340.034 .89

48.3r9 .824 . 8 2

100.49 per cent 100.44 per cent 101 .89 per cent

The phosphorus and fluorine of the original amblygonite hasalmost completely disappeared in crust and core. Most of thelithia, also, has been extracted from the core, but the crust contains2.64 per cent of that oxide. Alumina, an important constituent ofboth amblygonite and kaolin, has remained behind. Sil ica andwater have been introduced in fairly large quantit ies. The sevenper cent of potash in the core may be explained by the presence ofmica. Calculations on the constituents of the core indicate a

JOARNAL MINERALOGICAL SOCIETY OF AMEMCA 411

mixture of mica 52 per cent (muscovite 40 per cent, lepidolite12 per cent), kaolin 48 per cent and amblygonite 0.1 per cent.Calculated in the same way the green outer crust appears toconsist of about 41 per cent kaol in ,31 per cent lep idol i te ,0.3per cent amblygonite and 28 per cent bauxite.

CONCLUSIONS

The detailed study of the pegmatites at Buckfield and Green-wood has shown that at these two localit ies the original crystall iza-tion of the pegmatite magma resulted in an ordinary coarse grainedpegmatite made up chiefly of microcline, microperthite, andqvartz and containing subordinate apatite, green beryl, blacktourmaline, lepidolite, biolite, garnet, arsenopyrite, and ambly-gonite. After the crystall ization of the pegmatite the residualsolutions moved upward through the pegmatite, dissolved andreplaced the original minerals and deposited new minerals. Thefirst solutions deposited chiefly qtartz, clevelandite, Iepidolite,l ight colored beryl, and tourmaline, spodumene, apatite, and other

rare minerals.. Later solutions deposited rhodochrosite, ambly-gonite, and rare phosphates. The Iast hydrothermal solutionsdeposited chieflylepidolite, cookeite, qtrartz,apatite, and herderite.

A study of the literature and a brief field and laboratory examin-ation of the pegmatites at Mt. Mica and Auburn, Maine, showthat these pegmatites too were formed in successive stages, similarto those of the Buckfield and Greenwood pegmatites. The historythat can be worked out is no doubt fragmentary for all the depositsand in some more stages can be recognized than in others. AtMt. Mica the second hydrothermal stage was not found but atMt. Apatite, near Auburn, all three hydrothermal stages wererecognized.